The current dietary guidelines proposed by the United States Dietary Authority (USDA) for Americans through the years 2015-2020¹ should be modified based on accumulating evidence that contradicts some of their claims. To summarize, the recommendations emphasize a diet of whole grains, fruits, vegetables, low-fat or fat-free dairy, lean meats like poultry, fish, beans and nuts, and absolutely limiting the amount of saturated and trans fats, along with cholesterol, sodium and added sugars. The current recommendations echo similar sentiments that we’ve been hearing since the late 1950’s, after Ancel Keys performed some of the first observational studies regarding dietary fat and cardiovascular disease². The prevalence of obesity in the 1960’s was roughly 13% and has continued to rise in a near-linear fashion to 34% in the 2010’s³, under the stewardship of the USDA and the Food and Drug Administration (FDA). There are many factors that could’ve played an obesogenic role, such as changes in energy and nutrient density of foods, macronutrient composition, changes in processing and ingredients, and importantly, generally recommended dietary advice.

            There are numerous differences in the diets that our grandparents consumed compared to the Standard American Diet (SAD) of today, especially in regard to dietary fats. There has been a strong recommendation to reduce dietary cholesterol, based on studies conducted at the beginning of the 20^th century using rabbit models of atherosclerosis⁴. Rabbits were fed animal proteins and cholesterol dissolved in vegetable oil, and subsequently developed profound hyperlipidemia and atherosclerotic plaques in their arteries, but a rabbit does not consume many fats or cholesterol in its usual herbivorous diet. Until the 2015-2020 guidelines, the recommendation was to eat less than 300 mg/day¹ or 3 whole eggs per week, but new research has shed light on the fact that dietary cholesterol has little to do with atherosclerotic development⁵. The guidelines removed the 300 mg/day recommendation but still insist on eating as little cholesterol per day as possible. Randomized controlled trials have shown that those with metabolic syndrome that consumed 3 whole eggs per day compared to a yolk free substitute for 12 weeks actually had an improved lipid profile and increased sensitivity to insulin⁵. Cholesterol is also an important in the synthesis of sex steroid hormones, and high dietary cholesterol intake can help build lean mass and prevent sarcopenia in the elderly⁶, as well as promotes anabolic muscle growth in young adults following exercise at levels of even 800 mg/day⁶.

Evidence in favor of saturated fat consumption should also be taken into account, as new data shows that short and medium chain saturated fatty acids, such as those found in coconut oil and dairy products, can be beneficial in increasing HDL-C and insulin sensitivity, and decreasing plasma inflammatory markers⁷ which would decrease rate of cardiovascular events. It would not be wise to simply lump an entire class of macronutrient together into the same category, as they have vastly different effects on the body. The same can be said for trans fats; when produced industrially by the hydrogenation of vegetable and seed oils, they’re strongly associated with increases in coronary heart disease mortality, but when derived from ruminant meat sources like grass-fed beef, the association disappears⁸. The amount of vegetable oils and polyunsaturated fatty acids has exponentially increased in consumption over the last few decades, with some of the most common being canola and soybean oil. These oils are touted as being “heart healthy” and protective against CVD. However, mouse studies have shown consistently high levels of weight gain, fatty liver disease, glucose intolerance, and insulin resistance in mice fed a diet high in soybean oil compared to a diet high in fructose or coconut oil⁹. Some may also be familiar with the “French paradox”, whereby the French experience very low levels of CVD compared to other European countries despite a diet traditionally high in saturated fat¹⁰. Less familiar is the “Israeli paradox”, whereby Israelis experience paradoxically high levels of CVD, diabetes, obesity, and hypertension despite the highest polyunsaturated:saturated fat ratio diets in the world¹¹. The data suggests that the issue of which oils and fats and the amount of consumption are not as black and white as depicted in the health guidelines, and may even be the opposite of what is recommended.

This is not to say that their recommendations are entirely bad. They recommend consumption of fish, which should continue to be endorsed due to the very favorable fatty acid profile of oily marine fish like salmon and sardines. They are high in EPA and DHA, two omega-3 essential fatty acids that are needed for normal cognitive function¹³. Their emphasis on avoiding added sugars can help prevent people from overconsuming “hyperpalatable” foods. These are foods that elicit addiction-like behaviors that can dissociate caloric needs from the impulse to feed, leading to increased consumption. The foods that are most likely to create this “hedonic overeating” pattern of behavior are highly processed, very energy dense and high in added sugars, fats and salt¹⁴. More direct instructions should be made about the importance of avoiding processed foods in general. So-called “ultraprocessed” foods, described as, “cheap industrial sources of dietary energy and nutrients plus additives”¹⁵, are one of the main components of the SAD, and promote spontaneous overeating. Their main ingredients are typically cheap agricultural products like corn, soy, and wheat with artificial flavorings. These also activate hedonic food-seeking that facilitates obesity and the pathogenesis of disease.

      Overall, the diet has some good points, such as promoting the consumption of fish, vegetables and avoiding added sugars. The main issues that should be addressed with the dietary guidelines revolve around the recommendations for cholesterol and fats, and more suggestions should be made about restricting highly processed foods. The current data vindicates cholesterol as an important dietary nutrient, especially when consumed in high nutrient-density foods like eggs. Less importance should also be given to the polyunsaturated fats, as they may be implicated in the formation of chronic diseases and are a common food additive in processed foods. Lastly, more points deserve to be made about the value of locally produced whole-foods that promote satiety, health, and appropriate eating patterns.

References

1. https://health.gov/dietaryguidelines/2015/guidelines
2. KEYS, A, and F GRANDE. “Role of dietary fat in human nutrition. III. Diet and the epidemiology of coronary heart disease.” American journal of public health and the nation’s health vol. 47,12 (1957): 1520-30. doi:10.2105/ajph.47.12.1520
3. Hruby, Adela, and Frank B Hu. “The Epidemiology of Obesity: A Big Picture.” PharmacoEconomics vol. 33,7 (2015): 673-89. doi:10.1007/s40273-014-0243-x
4. Fan, Jianglin et al. “Rabbit models for the study of human atherosclerosis: from pathophysiological mechanisms to translational medicine.” Pharmacology & therapeutics vol. 146 (2015): 104-19. doi:10.1016/j.pharmthera.2014.09.009
5. Soliman, Ghada A. “Dietary Cholesterol and the Lack of Evidence in Cardiovascular Disease.” Nutrients vol. 10,6 780. 16 Jun. 2018, doi:10.3390/nu10060780
6. Lee, C. W., Lee, T. V., Vincent, C. W., Bui, S., & Riechman, S. E. (2011). Dietary Cholesterol Affects Skeletal Muscle Protein Synthesis Following Acute Resistance Exercise. The FASEB Journal, 25(1).
7. Coconut oil consumption improves fat-free mass, plasma HDL-cholesterol and insulin sensitivity in healthy men with normal BMI compared to peanut oil . Korrapati, Damayanti et al. Clinical Nutrition, Volume 38, Issue 6, 2889 – 2899
8. de Souza, Russell J et al. “Intake of saturated and trans unsaturated fatty acids and risk of all cause mortality, cardiovascular disease, and type 2 diabetes: systematic review and meta-analysis of observational studies.” BMJ (Clinical research ed.) vol. 351 h3978. 11 Aug. 2015, doi:10.1136/bmj.h3978
9. Deol, Poonamjot et al. “Soybean Oil Is More Obesogenic and Diabetogenic than Coconut Oil and Fructose in Mouse: Potential Role for the Liver.” PloS one vol. 10,7 e0132672. 22 Jul. 2015, doi:10.1371/journal.pone.0132672
10. Ghafari, Mahin et al. “Can French paradox hypothesis explain the observed different trends of mortality from ischemic heart disease and stroke in Western europe?.” International journal of preventive medicine vol. 4,12 (2013): 1345-6.
11. https://www.ncbi.nlm.nih.gov/pubmed/8960090
12. Wiss, David A et al. “Sugar Addiction: From Evolution to Revolution.” Frontiers in psychiatry vol. 9 545. 7 Nov. 2018, doi:10.3389/fpsyt.2018.00545
13. Thomas AB Sanders, Plant compared with marine n–3 fatty acid effects on cardiovascular risk factors and outcomes: what is the verdict?, The American Journal of Clinical Nutrition, Volume 100, Issue suppl_1, July 2014, Pages 453S–458S, https://doi.org/10.3945/ajcn.113.071555
14. Nansel, Tonja R et al. “Greater Food Reward Sensitivity Is Associated with More Frequent Intake of Discretionary Foods in a Nationally Representative Sample of Young Adults.” Frontiers in nutrition vol. 3 33. 18 Aug. 2016, doi:10.3389/fnut.2016.00033
15. Ultra-Processed Diets Cause Excess Calorie Intake and Weight Gain: An Inpatient Randomized Controlled Trial of Ad Libitum Food Intake

Hall, Kevin D. et al. Cell Metabolism, Volume 30, Issue 1, 67 – 77.e3