Popular enthusiasm for the Paleo diet, including a relatively high proportion of fat and protein presumed characteristic of the diet of our hunter/gatherer ancestors, has re-ignited the long standing debate about the nutritional merits of fat and carbohydrates, especially for athletes. In recent posts I have compared the effects of a high-fat diet with those of a high-carbohydrate diet on metabolic processes that have the potential to effect endurance performance, health and life expectancy. We have examined the evidence of these different diets on the development of preferential use of fat rather than carbohydrates for fuel during exercise; on risk of sustained elevation of the stress hormone, cortisol; on insulin resistance and inflammation; and on weight control. The evidence shows that a high fat diet does promote the use of fats as fuel during exercise, potentially beneficial in warding off disabling glycogen depletion during prolonged exercise. However both types of diet are associated with risks of sustained elevation of cortisol, insulin resistance and chronic inflammation. Particular components of each type of diet, specifically high glycaemic index (GI) carbohydrates which produce a rapid rise in insulin after ingestion, and omega-6 fatty acids, which are pro-inflammatory, are associated with high risk. With regard to weight control, the evidence indicates that low fat and low carbohydrate diets are equally effective. This post examines the evidence for effects on the ultimate outcomes: race performance, health and longevity.
Performance
When it comes to evidence regarding the effect of nutrition on performance, there are conflicting findings. In a meta-analysis of 20 studies comparing the effects of high fat with high carbohydrate diet on endurance exercise performance, Erlenbusch and colleagues found that averaged across all studies, subjects consuming a high-carbohydrate diet exercised significantly longer until exhaustion, but there were substantial differences between the findings of different studies, probably reflecting differences in the subjects studied and the design of the study. The benefit of the high carbohydrate diet was relatively large in studies of untrained subjects, but there was very little difference between the two types of diet in studies of trained athletes. In light of the fact that endurance training itself increases capacity for utilization of fats as fuel, it is plausible that in hitherto untrained subjects, a relatively brief period of high fat consumption is inadequate to produce a substantial capacity for fat utilization, so maximizing efficiency of glucose utilisation might be of greater value in such subjects.
There are some noteworthy studies that have reported greater benefit for a high fat diet in trained athletes. An early study from Tim Noakes lab in Capetown compared the effects of 2 weeks of high fat (70%) low carbohydrate (7%) diet with a high carbohydrate (74%), low fat (12%) diet in trained cyclists. The high fat diet led to higher fat utilization and improved performance at moderate exercise intensity, without deterioration of performance at high intensity. The importance of starting an endurance event with well stocked glycogen stores suggests that greater benefit might be obtained for a periodized nutritional strategy in which high fat diet is followed by a brief period of carbohydrate loading. A subsequent study from the Capetown lab using the nutritional periodization strategy found that high-fat consumption for 10 days prior to carbohydrate loading was associated with an increased utilization of fat, a decreased reliance on muscle glycogen, and improved time trial performance in a 20 Km time-trial following 150 minutes of medium intensity cycling.
Other studies of trained athletes reported equivocal results. Carey and colleagues tested the effect of fat adaptation using a nutritional periodization strategy, on performance during a one hour time trial following 4 hours of aerobic cycling. As expected the fat adaptation resulted in increased fat utilization. Power output was 11% higher during the time trial and distance covered was 4% greater, but this effect was not statistically significant. Nonetheless, in 5 of the 7 cyclists, the improvement in performance after fat adaptation was substantial, raising the possibility that the number of subjects was too small to provide adequate statistical power to test for a performance benefit.
Yet other studies indicated no benefit and perhaps even harm from the fat adaptation strategy. A further study from the Capetown lab by Haverman and colleagues compared 100km cycling time trial performance and also 1 Km sprint performance following 6 days of high fat consumption and 1 day of carbohydrate loading with performance following 6 days of high carbohydrate consumption and 1 day of carbohydrate loading. The anticipated enhancement of fat utilization was observed, but there was no significant difference between diets in 100-km time-trial performance, while 1-km sprint power output was significantly worse after the high fat diet. The investigators concluded that despite increasing fat utilization, the strategy of high fat diet followed by carbohydrate loading compromised high intensity sprint performance. This raises the possibility that the increased fat utilization might reflect impaired ability to use carbohydrates rather than an enhanced ability to utilize fats.
Thus, the tide of evidence has turned against the hope that fat adaptation produced by a period of one or two weeks of high fat consumption might be a worthwhile strategy for improving endurance performance. In contrast, this strategy might actually impair high intensity performance – an issue that is potentially of some importance even in events lasting several hours in which surges or hills might play a part in race outcome. The evidence does not rule out the possibility that some individuals might enjoy an improvement in endurance performance, but at this stage, the evidence does not justify a general recommendation of this strategy.
Perhaps improvement in performance from rather drastic dietary adjustments over a period of a few weeks is not the issue of greatest importance to the endurance athlete, for whom training is an undertaking extending over many months or years. Rather, the question of greater importance is the effect of long term nutrition on long term health. Although no studies have examined the long term effects of long term nutrition in endurance athletes, recent evidence has provided increasing clarity regarding the optimum diet for long term health in the general population.
Long term health and life expectancy
We will focus on evidence related to heart health because heart disease is the greatest cause of mortality in the general population and in addition there is some evidence that extensive endurance training and racing might in fact increase the risk of cardiovascular disease in athletes. Furthermore, most evidence suggests that a healthy diet for the heart minimises risk of cancer, though there are instances where foods that appear healthy for the heart have been linked to increased risk of cancer. Although depression is associated with only a modest risk of premature death, it is the illness causing the greatest degree of disability world-wide (according to the World Health Organization). Furthermore, mental state is of substantial importance in athletic performance. Therefore, I will also briefly address the evidence regarding the association between diet and depression.
Cardiovascular disease
In a recent comprehensive review of nutritional recommendations for cardiovascular disease prevention Eilat-Adar and colleagues found that both low fat and low carbohydrate diets are a healthy alternative to the typical Western diet. They note that low carbohydrate diets are associated with lower levels of potentially harmful tryglycerides and with higher levels of beneficial cholesterol in high density lipoprotein (HDL). Low-carbohydrate diets, which include 30%–40% of calories from carbohydrates and are low in saturated fat but high in mono-unsaturated fat, were found to be safe in healthy and overweight individuals at follow-up for up to 4 years. We will return to the controversial issue of saturated fat later. Eliat-Adar also found good evidence that Mediterranean diets, which include high consumption of fruit, vegetables and legumes, together with moderatley large amounts of fish but less red meat, may improve quality and life expectancy in healthy people, as well as in patients with diabetes, and heart disease. Mediterranean diets are preferable to a low-fat diet in reducing triglyceride levels, increasing HDL cholesterol, and improving insulin sensitivity.
A meta-analysis of trials by the Cochrane Collaboration – an organization which does extremely rigorous and conservative reviews of medical treatments – also concluded that evidence suggests favourable effects of the Mediterranean diet on cardiovascular risk factors, though with their usual caution, they stated that more trials are needed.
One trial that warrants special mention is the Spanish Prevención con Dieta Mediterránea (PREDIMED) trial, in which 7,216 men and women aged 55 to 80 years were randomized to 1 of 3 interventions: Mediterranean diets supplemented with nuts or olive oil and control diet. During a follow-up period of near to five years, nut consumption was associated with a significantly reduced risk of all-cause mortality. Subjects consuming more than 3 servings/week of nuts had a 39% lower mortality risk. A similar protective effect against cardiovascular and cancer mortality was observed.
With regard to the issue of saturated versus unsaturated fats, a recent re-analysis of the large and well conducted West Sydney Heart study found that replacing dietary saturated fat with omega- 6 linoleic acid, for subjects with known cardiovascular disease, actually led higher all-cause death rate, and higher death rate from coronary heart disease and cardiovascular disease. The authors also performed a new meta-analysis of previous studies and found that the pooled data also provided a strong trend towards higher death rate when saturated fat was replaced by omega-6 linoleic acid. This finding is contrary to the prominent advice to substitute polyunsaturated fats for saturated fats in worldwide dietary guidelines for reducing risk of coronary heart disease. The most plausible explanation is that the increased death rate is due to the pro-inflammatory effects of omega-6 fatty acids.
Cancer
The frequent reports in both popular press and the medical literature linking various foodstuffs to cancers of various types makes this topic a mine-field. In part this situation reflects the heterogeneity of cancer and the multiplicity of different factors that might contribute to the cause in different cases. Nonetheless, in general, the evidence indicates that diets that are healthy with regard to weight control and cardiovascular outcome tend to be associated with lower risk of cancer. For example, a recent large review found that adherence to the Mediterranean diet was associated with lower risk of certain cancers, especially cancers of the digestive tract, consistent with the finding from the PREDIMED study mentioned above. However, in light of the fact that a key difference between typical Western diets and the Mediterranean diet is the larger relative amount of omega-3 fats in the Mediterranean diet, it is noteworthy that some studies have reported that omega-3 fats are associated with increased rate of prostate cancer, while others have reported a decreased rate. This should encourage caution against simplistic conclusions that a food item is invariably healthy in all amounts and all circumstances.
Depression
Many studies using relatively low quality methodology to assess diet and/or mental state have reported an association between adherence to a ‘healthy’ diet and decreased risk of depression. More recently, several studies have addressed this issue using more rigorous methodology. A meta-analysis by Psaltopolou and colleagues of studies examining the association between Mediterranean diet and risk of various neurological and mental disorders found that the Mediterranean diet was associated with a decrease in risk of depression of approximately 30%. This reduction was very similar in magnitude to the reduction of risk of stroke and for cognitive impairment. However, association cannot establish cause, and it is possible that other life-style factors associated with adherence to a healthy diet account for the better physical and mental health. The most conclusive evidence comes for randomized controlled trials in which individuals are randomly allocated to different diets. In the PREDIMED trial, the group who were allocated to the Mediterranean diet augmented with extra nuts experienced a 20% lower rate of depression over a period of 3 years, compared with those on a low fat diet. This was not a statistically significant reduction. However, in those who had type 2 diabetes, the Mediterranean diet with extra nuts produced a 40% reduction in occurrence of depression which was significant. Thus the balance of evidence does suggest that a Mediterranean diet augmented by nuts produces a reduction which is significant at least in those who already show other evidence of adverse metabolic effects.
Synthesis
There is overwhelming evidence that diet plays a large role in health and longevity, and after many years of confusing debate, there is emerging clarity about the type of diet that is healthiest. This is neither a high fat/low carbohydrate Paleo diet nor a low fat/high carbohydrate diet. Rather, a substantial body of evidence suggests a Mediterranean diet is preferable, especially when augmented with extra nuts.
There is some variability between studies in what is taken to be the Mediterranean diet, but the consistent features include high consumption of fruits, vegetables and legumes (beans, nuts, peas, lentils); low consumption of red meat and meat products but substantial consumption of fish; near equal proportions of omega-3 and omega-6 fats; moderate consumption of milk and dairy products; and low to moderate red wine consumption. The status of grains and cereals is ambiguous. The Mediterranean diet adopted in PREDIMED included a high consumption of grain and cereals. In general, whole grains and cereals appear healthy though gluten sensitivity is an issue for at least some individuals.
While the evidence for the Mediterranean diet is largely based on studies of the general population with emphasis on heart health, rather than being focused on athletes, the disconcerting evidence that male athletes who have run numerous marathons over a period of many years are at risk of atherosclerosis (as discussed in detail in my post of 30th May, 2012) suggests that a ‘heart-healthy’ diet should be a high priority for endurance athletes.
When it comes to endurance performance, there is no clear evidence in favour of any particular diet. However the consistent evidence that a high fat/low carbohydrate diet promotes preferential utilization of fats during exercise appeared promising at first. It is disappointing that this apparently beneficial adaptation is not reflected in enhanced performance, even in ultra-endurance events. On contrast, there is actually evidence that it can harm high intensity performance, such as 1 Km cycling time trial performance. However, the fact that at least some individuals do appear to show an endurance performance benefit from a high fat diet (followed by brief duration carbohydrate loading) as observed in the study by Carey and colleagues, makes me reluctant to dismiss the potential value of at least moderately high fat consumption. One crucial issue is to identify why the clear evidence of improved fat utilization does not generally lead to enhanced performance. It appears that the fat adaptation strategy, at least in the form of a rapid increase in proportion of fat to a quite high level over a periods of a few weeks, is in some way harming the utilization of carbohydrates as much as it might be improving the utilization of fats.
In my opinion, one candidate mechanism by which high fat consumption might harm carbohydrate metabolism in muscle is the elevation of cortisol associated with the fat adaptation strategy used in the studies. One immediate effect of high cortisol is the decrease in accessibility of the glut4 transporter molecules that transport glucose into muscle. Furthermore, sustained elevation of cortisol can produce a decrease in sensitivity of glucocorticoid receptors that mediate the various effects of cortisol, including its anti-inflammatory effects, thereby possibly leading somewhat paradoxically to chronic inflammation. This is speculation on the basis of what is known about mechanisms rather than direct evidence of beneficial or harmful effects in practice. Nonetheless, it appears to me plausible that a gradual introduction of a higher proportion of fats, at least up to the modest levels in the Mediterranean diet, over a more sustained period might produce promote preferential utilization of fat during exercise in a manner that translates into improved endurance performance.
In light of the evidence that glycogen depletion during training can enhance training effects, I consider that during normal training, consumption of carbohydrates is potentially counter-productive, in most instances. Exceptions might include high intensity sessions; very prolonged sessions; or for the purpose of testing the planned strategy for race day in the final few long runs of marathon/ultra-marathon preparation. However, the need to start an endurance event with glycogen stores well stocked suggests that at least a brief period of carbohydrate loading, and ingestion of carbohydrates during long events, is highly desirable.
In summary, I consider that the emerging evidence provides strong support for the proposal that the optimum nutrition for most endurance athletes is a Mediterranean diet, but with carbohydrate loading immediately prior to long races.
Tags: cortisol, Mediterranean diet, Paleo diet
Canute's Efficient Running Site 
December 16, 2013 at 10:05 am |
Thanks Canute. A most thorough examination of the subjet. There was a show on Catalyst a couple of months back promoting the benefits of the Mediterranean diet. http://www.abc.net.au/catalyst/stories/2389833.htm
Also I read a Running Times story today in which Tracy Lokken says a ‘high protein/salad’ diet helped him run a PB marathon at age 47. He also improved after getting divorced, so maybe that helped the cortisol levels 😉
http://www.runnersworld.com/masters-profiles/tracy-lokken-consummate-competitor
December 16, 2013 at 9:52 pm |
Ewen, Thanks for your comment and for those links. Tracy Lokken is inspiring and appears to demonstrate that attention to details such as diet (and perhaps life stress) can pay dividends
December 16, 2013 at 10:48 am |
Hi Canute,
Thanks for another interesting essay into diet and health.
Once again I’m drawn to highlight that short studies on diet are not helpful in drawing longer term conclusions than the length of the study. The one week studies are far too short for full adaptations to show themselves. Full adaptations to fat burning don’t happen in one week or even two. Just because you are burning more fat at any one point in time doesn’t meant you are fully adapted to burning it efficiently, once you are well adapted the stress on the body will be lower and the compromises observed in the one week study will be greatly diminished if not disappear.
Another area that doesn’t quite add correlate with other data is the following your logic based on the quoted studies you suggest that a low carb/high fat diet would lead to long term and detrimental levels of cortisol that would impair fitness and lead to chronic inflammation. The other data I feel is important to square with is that observation that athletes find recovery better and less DOMS, this is some observed over long period of training on the diet. While you might cite this as anecdotal there are lot more athletes out there successfully applying a lower carb diet over longer terms than the number of athletes in the studies you have quoted cover.
I haven’t yet seen a complete explanation why lower carb athletes, including myself, have observed quicker recovery. It would suggest to me that the body is under less stress and is suffering less with inflammation. It could be that lowering the consumption of high GI carbs is what is the key. It could be that the glycogen stores are cycled less deeply when training so the response from the immune system isn’t as strong. It could it be simply that Cortisol levels do indeed remain higher over the longer term and this has as the usual anti-inflammatory effect, but crucially the deterioration of cortisol sensitivity doesn’t happen like one would expect in a high carb athlete so the lower carb athlete doesn’t observe the negative consequences.
Or could it be simply eating less carbs means eating less toxic foods is the key. We know that sugar and in particular fructose is toxic in large quantities, as is omega-6. Proteins in plant and protein in diary foods can also be toxic. Cooking at high temperatures can also render food toxic. Conversely some foods are toxic when raw but safe when safe when cooked properly. Could it be eliminating toxicity could the key to reducing chronic inflammation?
Another converse is a little bit of toxity can be a good thing, keeps our immune system active and can actually form part of immune system. Perhaps eating too much of any one food type can be part of the problem, compounded what low levels of toxicity there might be in the foods and limiting the range of minerals and vitamins we get from them.
As usual more questions that answers 😉
December 16, 2013 at 9:56 pm |
Robert
We agree that studies of short term adaptation to a high fat diet would not be expected to reveal the benefits that might be produced by longer term more gradual adaptation. However, your focus on the 1 week studies fails to take account of the fact that the potential adverse effects such a sustained elevation of cortisol are also seen after 4 weeks of fat adaptation (eg Ebberling et al; ,Venkatraman et al, referenced in my previous post). It is also noteworthy that the studies showing impairment of performance after high fat consumption include studies ranging from 1 week (Haverman et al, this post) to 7 weeks (Helge et al, J Physiol. 492 Pt 1:293-306; 1996). I had not previously mentioned Helge et al because they only tested performance during moderately intense exercise at 81% of VO2max. Nonetheless, one interesting feature of the Helge study is that noradrenaline was elevated during exercise after 7 weeks of high fat diet. Noradrenaline is a potent promoter of glycogen breakdown. Helge et al found that muscle glycogen breakdown was as large in the high fat group as in the group who consumed a high carbohydrate diet for 7 weeks, suggesting that the increased noradrenaline might have negated the benefit from increased ability to utilise fats.
So I think the balance of existing evidence from formal studies provides very little evidence to support the hope that a high fat diet will increase endurance performance. However, as indicated my post, I remain hopeful that if one could avoid the rise in ‘stress’ hormones (cortisol; noradrenaline; adrenaline) it might be possible to translate the benefit of increased fat utilization into improved endurance performance.
Like yourself, I am impressed by anecdotal evidence that fat adaptation can be beneficial, though evaluation of anecdotes also requires attention to detail. In your own case, it is clear that you have run very well in ultras this year. However I also note that you stated that the need to fit in with family meals has prevented you from following a ketotic diet. Have you estimated what proportion of calories you have been obtaining for fat, protein and carbohydrate in recent months? What are the key differences between your recent diet and a Mediterranean diet, apart from less cereal and grains? Granted that you have raced so well, I wonder if perhaps you should thank your family for discouraging you from a very strict high fat diet 😉
I agree that sugar and also cooking at high temperature should be avoided wherever possible
December 17, 2013 at 9:33 am
I haven’t yet measured the calories composition of my current diet. The exact balance varies from day to day, week to week depending on what we are doing as a family.
In general I’d like to aim for a 50% fat, 30% carb, 20% protein mix. Previously I was probably nearer 60% carb, 20% fat and 20% protein. Both these sets of figures are just guesses.
The clearest changes are in that I now skip breakfast for 5 to 6 days a week, previously breakfast would have been a high carb meal. During the week for lunches we often don’t consume too much in the way of carbs, but weekends with our girls back from School this does slip. Evening meals with the whole family we haven’t changed our diet significantly, it’s more a slow process of introducing new foods and stressing others less.
I’ve made it a bit of hobby trying to come up with high fat modest sugar deserts for the family. All our children now really enjoy 70% dark chocolate which helps a lot, but it does mean that Julia and I now have competition for good chocolate when we treat ourselves!
Another change is that when I do consume carbs I try to consume them with fat and/or protein to slow down digestion and reduce the GI of the meal.
Now I’m training for the West Highland Way Race I am trying to get more strict with not consuming high GI snacks (kit-kats, biscuits etc.), instead opting for fruit and nuts for snacks.
The whole family are reporting that really sweet foods now don’t taste as appealing as they once did. There is still a long way too go though, modern society is just so geared up to pushing sweet high carb, high GI food everywhere you look.
I am enjoying my food now more, no longer do I demonize fats and try to avoid them, instead I have embraced healthy fats, so rich sauces and deserts can be relished and enjoyed. Rather than be put off my the clotted cream of cream team I’ll view the cream as one of the most healthy parts of the treat. Same goes for fat on meat, I’ll enjoy it along with the rest of the meat rather than cut it off and discard. When cooking with olive oil or coconut fat I’ll make sure that I pour the remaining juices/oil over my meal to not waste them – there are lot of minerals that leech out into the juices so it’s important to consume them for general health too.
In terms of proportions I don’t know what the range is for what is considered to be the “Mediterranean Diet”. I’d guess I’m probably not a long way off it. I feel I’ve more corrected my diet to be more well balanced than specifically being low carb.
December 17, 2013 at 11:48 am |
Robert
Thanks for those details of your nutrition. I agree that most of those features are healthy. The clearest beneficial change is the reduction in high GI carbs. You do not describe a specific focus on legumes, which I regard as an important feature of the Mediterranean diet. I think you are probably consuming more fat that in the typical Mediterranean diet and possibly more red meat. The interesting issue is the proportion of different fats. The impression created by your choice of cooking oils implies you are selecting saturated fats in preference to omega-6 fats. This fits with the findings of the West Sydney Heart study and other recent evidence suggesting that at least in the context of typical Western diets, excess of omega-6 fats is more dangerous than excess of saturated fat.
Good luck with the WHWR. I think that for an event of that length, getting body metabolism right is a major priority.
December 17, 2013 at 5:08 pm
Hi Canute,
I eat red meat at most a couple of times a week, I’d be surprised if I consume more than a Mediterranean diet. Chicken I might eat once or twice a week. With the Chicken we roast it and have it as roast meal, then I boil the carcass as stock to use for soup for following days. I try to have liver once a week, but often have to settle for liver pate.
W.r.t legumes, I now generally try to avoid them. There are safer and more nutritious forms of protein that I can consume so am happy to do so.
Same with wheat, I can afford to eat more healthy forms of carbs so now avoid wheat based products for most days of the week. Out kids love pasta and bread so it’s hard to reduce wheat products from the diet for everyone.
I prefer to have starchy root vegetables and rice for carbs as these don’t have the potential anti-nutritious and toxic payloads of legumes and wheat.
The following article dives in the raw data from the China Study to see if there are other explanation for the strong correlation between wheat and mortality that appears in the data:
http://rawfoodsos.com/2010/09/02/the-china-study-wheat-and-heart-disease-oh-my/
It could be that wheat is only high risk for certain people, but why play roulette with a loaded gun when you have other alternatives?
I do have to admit to soft spot for home made pancackes that I make for the girls at the weekend, so I often dig in with them. I also still eat pasta when it’s on the table because it’s just plain awkward to avoid it when the rest of the family are eating it. I also on occasion have deep fried bread. So even though I aim to avoid wheat it’s still part of my diet 2 to 3 days each week. That’s down from near 7 days a week.
We have moved across from margarine and sunflower oil to butter and oliver oil, coconut oil and ghee for cooking.
I also eat more eggs. I also consume less milk, but eat more diary fats in the form of cream, cheese and full fat home made yoghurt. We also now make Kimchi (fermented cabbage) it’s a great source of vitamin K12.
I have eaten plenty of vegetables so I haven’t need to make changes here. I eat a bit more fruit and nuts but neither form a staple of my diet.
I eat fish two to three times a week, perhaps up slightly on before, but not by much.
In many ways this is a move towards or perhaps beyond the Mediterranean diet. While the Mediterranean diet does look to be generally healthy compared to other diets tested in various studies I certainly don’t think is a reason to assume it’s the perfect diet.
I have no doubt that my current diet is healthier than it was before. Whether my success in my training and ultras is down more to the general improvements in the diet (more nutritious, less toxic) or simply down to eating less carbs/more fat I can’t say. My guess it’s a bit of both.
There are still things I can improve with my diet, in terms of health I don’t feel reducing carbs further will be of particular benefit. If I had a form of metabolic syndrome I’d think differently, but I’m healthy and certainly retain plenty of insulin sensitivity so moderate amount of healthy carbs shouldn’t be a risk factor.
Over the next six months I’ll keep tweaking my diet to contain more of the good stuff and less of the riskier elements. I’d guess I’ve probably fixed the biggest risk factors for long term health so further significant benefits are unlikely.
December 18, 2013 at 12:57 am |
Robert,
If you are sparing with the red meat; eat fish several times a week; and also some chicken, then I suspect your meat consumption might be fairly typical of the Mediterranean diet. Liver is certainly an excellent source of many micronutrients. When I was training regularly 50 years ago, lambs fry once a week was the only special ingredient I added to the somewhat randomly mixed diet that I had consumed since childhood.
While legumes are usually regarded as part of the Mediterranean diet, the finding from the Predimed study that adding extra nuts to the ‘typical’ Mediterranean diet substantially enhanced the reduction in ‘all-cause’ mortality indicates that nuts are especially healthy. Given the choice of nuts or beans, I would choose nuts.
The question of grains, and wheat in particular, is the most controversial aspect of the Mediterranean diet. There is an interesting review of the possible role of wheat and other cereals in chronic inflammation by Karin de Punder and Leo Pruimboom in ‘Nutrients’ (Nutrient 5, 771-787; 2013). They conclude that the wheat grain agglutinin and gliadin increase intestinal permeability and activate the immune system, thereby promoting inflammation. On the other hand an article in ‘Diabetes Care’ by Lu and colleagues (Diabetes Care 29:207–211, 2006) examined indices of inflammation in nearly 1000 nurses in the Nurses Health Study and concluded that whole grains and a low–glycemic index diet may reduce systemic inflammation among women with type 2 diabetes. So the evidence is somewhat inconsistent. I am not sure what to make of the data about wheat from the China study because there are potentially so many variables that might influence the interpretation of that data. Nonetheless, I am inclined to agree that it is probably sensible to avoid wheat as far as possible. I myself consume a moderate amount of oats while minimising intake of wheat.
I certainly would not claim that Mediterranean diet is ‘perfect’ but I think the evidence indicates that overall, it is a good guide, and in particular a good guide to the optimum types and proportions of fats and carbs, though the needs of individuals will differ.
December 18, 2013 at 9:54 am
Hi Canute,
I agree the Mediterranean diet looks to be pretty healthy, the less healthful aspects being compensated by the healthful aspects. If you are going to start anywhere with a diet the Mediterranean diet is probably a good starting place.
W.r.t the whole grains and the Nurses Health Study, could it be replacing non whole grain with whole grain improves health markers making it tempting to conclude that whole grain is healthful. However, unless you compare against not eating grain you don’t get to find out whether whole grain is in fact healthy for you.
In effect what you see is that if you replace that something is very bad for you with something that is just bad for you you will see a health improvement, but it doesn’t actually mean that the bad thing is good.
In terms of optimum balance of fat/carbs/protein one approach is to look at the composition of milk and then tweak it to take into account that at different stages of life we need less or more of different components. For instance children need more polyunsaturated fats to aid new cell growth, so moving to an adult one would expect to need less polyunsaturated fat than is in raw milk. The same goes for carbohydrates, children will need more than adults.
A quick search on the web pulls up for cows milk:
http://www.raw-milk-facts.com/what_is_in_raw_milk.html
49% fat, 29% carbohydrate, 22% protein
For human milk:
https://en.wikipedia.org/wiki/Human_breast_milk
54% fat, 40% carbohydrate, 6% protein
I’m a bit surprised by how much more protein cows milk has than human, is it that we grow slower and need less? Or are these two sets of figures now quite accurate?
These figures when we start life we require 35% more calories from fat than carbohydrate and as life goes on and we grow less we’ll likely require less dependant on carbohydrate and protein.
It’s worth mentioning that only 14% of the fat in human milk is polyunsaturated, which is 7.5% of total calories and so should be seen as upper limit of how much polyunsaturated fat might be OK to consume, given adults aren’t growing the figure should likely be significantly lower.
To me a target of 50% calories from fat seems a good starting point and likely shouldn’t be lower than this.
December 18, 2013 at 6:39 pm |
Robert,
Yes it is possible that in the Nurses Health Study the apparent benefit of reduced inflammation with increased consumption of whole grains might have reflected replacement of other harmful foods such as high GI carbs, by whole grains that are less harmful, but harmful nonetheless. One of the reasons why the Chinese data on adverse effects of wheat is potentially important is that in China, it is possible to compare outcome in wheat consumers with outcome in people who consume virtually no wheat, but largely low GI forms of rice instead. However, while the Chinese data should be taken into account when weighing up the balance of evidence, the interpretation of that data might be confounded by potentially important differences in how the wheat is prepared for consumption; effects of differences in total calorie intake (likely to be non-linear); differences in micronutrient availability (also likely to be non-linear) and perhaps even population genetic differences.
You are right in emphasizing changes in nutritional requirements across the lifespan. At both ends of the life span, ensuring that nutrition meets the needs for building new tissues (anabolism) assumes greater importance relative to the need to the supply the fuel to meet energy requirements (catabolism), than in young and mid-adult life.
The high fat content of human breast milk is consistent with the fact that the unique characteristic of humans is an extremely complex brain, in which there are more than 100 billion neurons, connected by about 200,000 Km of ‘wiring’. Each neuron makes many thousands of connections with other neurons. The cell membranes of these neurons are predominantly composed of lipids, together with some rather sophisticated proteins and saccharides. These membranes are not mere passive envelopes, but are complex structures that perform electrical and chemical signalling. Building these membranes requires specialised lipids, some of which cannot be synthesized in the human body and hence must be derived from diet. Although the human head and brain is already quite large at birth (making child-birth a tricky business), the complexity of the wiring develops massively during childhood. The amount of wiring increases dramatically in early childhood and is followed by a period of extensive remodelling of the connections, together with insulation of the long fibres with layers of myelin. Thus in infancy and to some extent throughout childhood, the really crucial nutrient is fat to ensure a plentiful supply raw material for membranes and myelin.
In contrast for the elderly, loss of muscle is a problem and adequate dietary protein becomes a more crucial.
December 19, 2013 at 2:14 pm
Thanks for the details about childhood brain growth dependence on fat. Would the modern high carb diet that modern western children live off be holding back brain development?
In terms of relative proportions of fat/carb/protein, surely the growth in mass of the rest of body is larger than for the brain as the portions of a babies head to body size is higher than that of the child let alone an adult.
I guess one has to look at weight of nutrient consumed rather than calories consumed when thinking about growth rather than steady state, from a weight perspective human milk has more carbohydrate than fat.
Do know of good estimates for the relative abundance of fat/carb/protein that goes to make up a human in different stages of life?
Of course diet proportions don’t map to body composition as most of what we eat is used as fuel and repair rather than growth. Obviously adults will hopefully obtain a relative static balance of body composition save for interventions like pregnancy 🙂
Um… perhaps using human milk as guide isn’t perfect. I do still believe it’s a useful starting place though.
December 19, 2013 at 7:40 pm |
Robert,
Yes, the increase in weight of the brain will only be a minor fraction of total body weight gain, though there is a large amount of remodelling in the brain that requires the construction of specialised membranes, incorporating lipids. Some of these lipids cannot be synthesized in the body, so there is need for a generous supply of fats to ensure that the essential lipids are available. In many parts of the body amino acids will be required for incorporation in protein and some of these are also essential amino acids that cannot be synthesized in the body, so it is a bit surprising to me that human breast milk has a relatively small proportion of protein. However, in the early months of life, gain in fat mass is substantially greater than gain in protein. Some of the infant fat is brown fat, required to keep the infant warm.
The proportion of energy required for growth decreases fairly rapidly during the first year of life. In the first few weeks, about 40% of energy is utilised for growth; over the first three months, the average proportion of energy utilized for growth is about 35%. Because the nutritional needs of infants differ from those of adults, the composition of breast milk is not a good guide to adult nutritional requirements.
As for the question of whether modern formula infant feeds provide enough of the fats essential for synthesis of neural membranes in the brain, there is evidence that breast feeding in the early months produces greater brain growth ( see for example http://www.sciencedirect.com/science/article/pii/S1053811913005922 ) and also a small but significant enhancement of cognitive development even after allowing for socio-economic status and other relevant variables (see for example, https://www.iser.essex.ac.uk/publications/working-papers/iser/2010-40.pdf ).
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Traiteur Rabat Regal; Traiteur de ronome au Maroc
Traiteur Rabat Regal au Maroc