Last week, Yoni Freedhoff highlighted a great JAMA editorial by Dariush Mozaffarian and David Ludwig entitled “Dietary Guidelines in the 21st Century-a Time for Food.” (1). It is a short but smart commentary by 2 researchers who clearly see the big picture (and have contributed research to support it): that we should be promoting whole foods, not specific nutrients which push consumers toward processed products. Yoni has reprinted most of it on his blog, so I will make a very short summary here:
- Nutritional science began by preventing many deficiency diseases, and in that has been a great success.
- RDAs were eventually created to prevent nutrient deficiencies.
- The last few decades of the last century saw an increase in many diseases of modernity, and along with them recommendations for specific nutrients to attempt to mitigate disease risks.
- RDAs are inadequate and irrelevant for the purpose of “dietary optimization.”
- Saturated fat per se doesn’t seem to be related to heart disease, individual nutrients largely fail to have measurable effects in clinical studies, and dietary guidelines recommend a diet of mostly carbohydrate, which is not only unnecessary in human diets, but carbohydrate qualities and sources vary dramatically.
- Information on food labels “nutrition facts” does not generally help consumers choose foods for good health- the real foods (fruits, vegetables, real meats and so on) tend not to have nutrition facts anyway.
- Specific foods and dietary patterns, unlike individual nutrients, do correlate consistently with reduced disease risks, which likely reflects a complex synergy of structure, preparation methods, and the thousands of nutrients in real foods.
- Marketing and fortification has given health halos to certain processed foods, skewing public perception of what is a healthy food.
- We should move toward food-based instead of nutrient-based dietary guidelines.
Here are some of the most recent studies that support these contentions:
Micha, Wallace, and Mozaffarian (2) performed a meta-analysis that suggests red meat is not associated with coronary heart disease or diabetes mellitus, while consumption of processed meats significantly increased risk for both.
Siri-Tarino, Sun, Hu, and Krauss (the man who discovered lipoprotein subfractions) (3) published this year the results of a large meta-analysis of prospective cohorts that suggests saturated fat is not associated with coronary heart disease or cardiovascular disease risk.
So what happens when recommendations suggest saturated fat and replacing it with other macronutrients?
Jakobsen et al. (4) found in a prospective corhort that replacing saturated fat with low-glycemic index carbohydrate lowered risk of myocardial infarction, but substituting it for high-glycemic index carbohydrate increased risk. Which do you think most Americans consume? NHANES survey data suggests whole grain intake is less than 1 serving per day.
Mozaffarian et al. (5) published a meta-analysis of 8 randomized, controlled trials that suggest a 19% reduced risk of coronary heart disease events when saturated fat was substituted for PUFA- risk reduction was evidence with an average PUFA consumption of 14.9% of total energy intake compared to 5%.
So perhaps saturated fats do have some negative effect, which future studies will have to further explore. But it seems that processed carbohydrate may be the true culprit. Hu (6) makes a case for this discussing these recent studies in a recent AJCN editorial, and Siri-Tarino, Sun, Hu, and Krauss published a large review (7) in the same issue that concludes similarly- that refined carbohydrate seems particularly harmful.
Epidemiological studies are difficult to draw conclusions on, but further support comes from many recent interventional trials that suggest replacing carbohydrate for fat in many contexts improves cardiovascular risk markers (see ref 7 and most recent this month here by Krauss and colleagues).
While clearly there is much disagreement on the “ideal” diet in terms of macronutrients (and it likely doesn’t exist for everyone), one thing that nearly everyone will agree on is that shifting to real foods over processed ones will bring dramatic improvements in health because they better align with what research shows will reduce risks. Cultures that have not developed often enjoy low rates of chronic disease. Consuming diets with whole foods generally leads to a pretty balanced macronutrient intake anyway, which lowers the need to worry about details. I like the rule of going mostly for foods that don’t have nutrition facts panels at all- those that are generally toward the outside of grocery stores.
While nutritional science at the nutrient and molecular level is fascinating and making incredible progress, I think the most effective way to reverse health epidemics is to focus on education about foods and changing the nutritional environment.
1. Mozaffarian D, & Ludwig DS (2010). Dietary guidelines in the 21st century–a time for food. JAMA : the journal of the American Medical Association, 304 (6), 681-2 PMID: 20699461
2. Micha R, Wallace SK, & Mozaffarian D (2010). Red and processed meat consumption and risk of incident coronary heart disease, stroke, and diabetes mellitus: a systematic review and meta-analysis. Circulation, 121 (21), 2271-83 PMID: 20479151
3. Siri-Tarino PW, Sun Q, Hu FB, & Krauss RM (2010). Meta-analysis of prospective cohort studies evaluating the association of saturated fat with cardiovascular disease. The American journal of clinical nutrition, 91 (3), 535-46 PMID: 20071648
4. Jakobsen MU, Dethlefsen C, Joensen AM, Stegger J, Tjønneland A, Schmidt EB, & Overvad K (2010). Intake of carbohydrates compared with intake of saturated fatty acids and risk of myocardial infarction: importance of the glycemic index. The American journal of clinical nutrition, 91 (6), 1764-8 PMID: 20375186
5. Mozaffarian D, Micha R, & Wallace S (2010). Effects on coronary heart disease of increasing polyunsaturated fat in place of saturated fat: a systematic review and meta-analysis of randomized controlled trials. PLoS medicine, 7 (3) PMID: 20351774
6. Hu, F. (2010). Are refined carbohydrates worse than saturated fat? American Journal of Clinical Nutrition, 91 (6), 1541-1542 DOI: 10.3945/ajcn.2010.29622
7. Siri-Tarino PW, Sun Q, Hu FB, & Krauss RM (2010). Saturated fat, carbohydrate, and cardiovascular disease. The American journal of clinical nutrition, 91 (3), 502-9 PMID: 20089734