Over the last five decades there has been a substantial increase in obesity, diabetes, cardiovascular disease, and other so-called lifestyle diseases in Western societies. This has resulted in an increase of research regarding how individuals can make their diets healthier (e.g., references 1-5). Changing the contributions of the three macronutrients –protein, carbohydrates, and fat – to people’s diets has been argued to be one way of reducing the probability of experiencing lifestyle diseases (references 6 and 7). However, at the moment there is little consensus regarding the percentage of an individual’s diet that each macronutrient should comprise. The US government recommends that 10-30% of dietary calories should come from protein, 45-65% from carbohydrates, and 25-35% from fat (reference 8), but many other macronutrient targets have been put forward in the last few decades (e.g., references 9-11).
In addition to scientifically researched macronutrient targets, there is what seems to be a never-ending creation of 'fad diets', each of which propose a different macronutrient target to help you reach your weight and health goals (think Keto, low-fat, Atkins, etc.). For my MA thesis, I investigated the macronutrient claims of one such fad, the Paleo Diet. This diet claims that we can improve our health by eating food items that replicate the macronutrient distribution of the diets of humans who lived before the invention of agriculture in the Neolithic period. The idea being that the obesity and lifestyle disease epidemic is cause by a 'mismatch' between humans' evolved physiology and the highly processed agricultural diets that most people in Western societies consume. By returning to 'our Paleolithic ways' (aka a Paleolithic diet), humans can supposedly reverse obesity, diabetes, and other lifestyle diseases. The macronutrient split that the Paleo Diet proposes is 19-35% protein, 22-40% carbohydrates, and 28-58% fat -- quite different from what is proposed by the US government and WHO guidelines.
I'll save an evolutionary critique of the Paleo Diet and the specificities of my study for another post. For the purposes of this post, I will keep things simple. Much like there isn't one diet to rule them all, as I discussed in my last post, the literature that exists does not support one ideal macronutrient target for humans. There is evidence to suggest that there are upper and lower limits for protein consumption, but the range is extremely wide and varies with body size, muscle mass, and habitual protein intake (e.g., reference 12). Regarding carbohydrates and fat, there is no good data to suggest a specific target; however, there is data to suggest that each of these macronutrients are important and if you omit either (I'm looking at you Keto and 80-10-10 diet) you risk compromising your long-term health (references 11 and 13).
There are certainly cases where individuals do function better on a higher/lower carb, higher/lower fat, or higher/lower protein diet, but this is highly individual. Ultimately, a relatively balanced amount of each macronutrient is important as there are negative effects of too low and potential too high amounts of each macronutrient (references 11-13). Until further research is done, the WHO, US, and Canadian guidelines are a good place to start. If weight loss is your goal, protein increases satiety and might be useful to increase (reference 12). If endurance or optimal brain function is your goal, carbohydrates are key (the brain runs on glucose) (reference 11). Ultimately though, you don't need to worry too much about your macronutrients as long as you are eating enough, but not too many, calories (references 4 and 5).
References:
1. Albenberg, L. G., and Wu, G. D. (2014). Diet and the Intestinal Microbiome: Associations, Functions, and Implications for Health and Disease. Gastroenterology, 146(6), 1564–1572.
2. Estruch, R. et al., (2013). Primary Prevention of Cardiovascular Disease with a Mediterranean Diet. New England Journal of Medicine, 368(14), 1279–1290.
3. Lichtenstein, A. H. et al. (2006). Diet and Lifestyle Recommendations Revision 2006. Circulation, 114(1), 82–96.
4. Swinburn, B. A. et al. (2019). The Global Syndemic of Obesity, Undernutrition, and Climate Change: The Lancet Commission report. The Lancet, 393(10173), 791–846.
5. Willett, W. et al. (2019). Food in the Anthropocene: the EAT–Lancet Commission on healthy diets from sustainable food systems. The Lancet, 393(10170), 447–492.
6. Acheson, K. J. (2013). Diets for body weight control and health: the potential of changing the macronutrient composition. European Journal of Clinical Nutrition, 67(5), 462–466.
7. Solon-Biet, S. M., Mitchell, S. J., de Cabo, R., Raubenheimer, D., Le Couteur, D. G., and Simpson, S. J. (2015). Macronutrients and caloric intake in health and longevity. The Journal of Endocrinology, 226(1), R17-28.
8. HHS, and USDA. (2015). Dietary Guidelines for Americans 2015-2020: Eighth Edition. https://doi.org/10.1002/9781118889770.ch2
9. Brunner, E. J., Wunsch, H., and Marmot, M. G. (2001). What is an optimal diet? Relationship of macronutrient intake to obesity, glucose tolerance, lipoprotein cholesterol levels and the metabolic syndrome in the Whitehall II study. International Journal Of Obesity, 25, 45.
10. Cordain, L., Brand-Miller, J., Eaton, S. B., Mann, N., Holt, S. H. A., and Speth, J. D. (2000). Estimations in Worldwide Hunter-Gatherer Diets. American Society for Clinical Nutrition, 71, 682–692.
11. Seidelmann, S. B. et al., (2018). Dietary carbohydrate intake and mortality: a prospective cohort study and meta-analysis. The Lancet Public Health, 3(9), e419–e428.
12. Wu, G. (2016). Dietary protein intake and human health. Food and Function, 7(3), 1251–1265.
13. Ludwig, D. S. (2016). Lowering the bar on the low-fat diet. JAMA - Journal of the American Medical Association, 316(20), 2087–2088.