Diet - Optimum Nutrition

Nutrition is complicated, and there is no way to make it simple! I believe, as do many experts, that efforts to make nutrition simple led to the schematic in 1992 of a USDA food pyramid which in hindsight contributed to the obesity epidemic in the US. While the 2005 USDA 'MyPyramid' (really a trapezoid) and the subsequent 2010 USDA 'MyPlate' represent significant conceptual improvements as compared with the 1992 Food Pyramid, I believe that the Healthy Eating Food Pyramid, initially developed by Dr. Walter Willett in the 1990’s, and printed in revised form in his book Eat, Drink, and Be Healthy (2001) offers a healthier pictorial guide to optimum nutrition.

An important principle of nutrition is that the foods we eat may affect hormonal balance in the body. For years, I believed that ‘a calorie is a calorie is a calorie,’ a simplistic concept which can be labeled as the 'biochemical paradigm.' I now realize that the type of carbohydrate consumed (i.e. glycemic index) is important in part because of the hormonal effect of various forms of carbohydrates upon insulin levels. Additionally, the ratio of omega 3 fatty acid to arachidonic acid content of the diet is important because of the hormonal effect of these fats on eicosanoid (i.e. prostaglandin, leukotriene) hormone levels. The concepts of the type of polyunsaturated fat intake as it relates to eicosanoid synthesis and the glycemic index of carbohydrates as it relates to insulin secretion will be addressed more fully in the body of this article.

A second important principle of nutrition is the principle of balance, moderation, and variety of nutritional intake. All food at a reductionist biochemical level consists of three macronutrients - carbohydrate, fat, and protein. Each time one eats (meal or snack), the individual should strive to achieve balance amongst the intake of carbohydrate, fat, and protein. Optimum nutrition from a public health perspective translates to consuming a wide variety of fruits and vegetables (eating the rainbow of colors), eating a wide variety of whole grains, eating a wide variety of nuts and seeds, consuming modest amounts of fish and extra-virgin olive oil, and limited quantities of meat, poultry, dairy, processed foods and snack foods (a caveat is that these general principles may need to be modified for individuals with specific medical conditions/diagnoses or food sensitivities - this individualization is done in the context of an office visit with a knowledgeable health care practitioner).

Fat – some fat intake is essential for life; omega 3 and omega 6 fatty acids (both polyunsaturated fatty acids) cannot be synthesized in the body by humans and thus must be consumed in the diet. Bottom line in 2024 is that fat as a general entity is neither good nor bad – one must examine each type of fat separately, as outlined in the next few paragraphs. Remember, nutrition is not simple!

There is decades-long universal agreement amongst nutrition experts that artificial trans fat intake is unhealthy. Trans fat intake not only raises the blood cholesterol level, but also lowers the HDL cholesterol, the good fraction of cholesterol in the blood. While some trans fats such as CLA do exist in nature, most trans fats are fats which have been chemically altered to improve shelf life or to make a fat that would otherwise be liquid at room temperature into a solid at room temperature. Trans fat is present in some snack foods, some breads, some breakfast cereals, and some peanut butters. Based on a growing public awareness of the adverse health effects of trans fat, and (appropriate) government regulatory agency pressure, there is an ongoing (2020s) concerted effort by manufacturers of food to eliminate trans fats from food. Effective on January 1, 2006, the trans fat content of foods is listed in the ‘Nutrition Facts’ box on the label. The only caveat with regard to this requirements is that food with less than ½ gram of trans fat per serving can list the trans fat content as ‘0’ on the ‘Nutrition Facts’ box, even though there is a small amount of trans fat in the food. In foods with less than ½ gram of fat per serving, the trans fat content will be reflected only in the ingredients list – look for the words ‘hydrogenated’ or ‘shortening’ as an indication of trans fat in the food. Bottom line in 2024 is that it is best to avoid all artificial trans fat intake.

There is disagreement amongst nutrition experts regarding the extent to which saturated fat intake should be restricted; I believe that there is a general consensus that saturated fat in the diet does raise the total cholesterol in the blood without significantly affecting the HDL (good) cholesterol fraction, and that saturated fat intake should be restricted to 7-10% of total calorie intake per day. In the 2015 Dietary Guidelines for Americans (these guidelines are updated by the government every 5 years), saturated fat is no longer listed as a "nutrient of concern."  Saturated fat is found in red meat, the skin of poultry, dairy products, and tropical oils (palm and coconut oil). Current data indicates that in terms of adverse influence on blood cholesterol levels, the saturated fat in dairy is worst, the saturated fat in meat less bad, the saturated fat in tropical oils even less bad, and the saturated fat in chocolate is best (the stearic acid in chocolate is metabolized in the body into oleic acid, a monounsaturated fat). However, while dairy intake is detrimental from the perspective of effect on the lipid profile, scientists now know that there is a type of fat called sphingolipids in dairy that has heart protective effects. Sphingolipids are plentiful in cheese, and this might explain population data which shows a correlation between moderate intake of cheese and a reduced risk of heart disease and stroke. Bottom line in 2024 is that there is conflicting scientific information on health effects of saturated fat; modest limitation of intake is likely sufficient for most individuals but marked limitation of intake may be beneficial in those with a diagnosis of coronary artery disease.

Monounsaturated fat, present in avocados, olives, olive oil, and a variety of nuts and seeds, is healthy – intake in amounts of 10-15% of total calorie intake per day is recommended by many nutrition experts. The Mediterranean diet, shown in many scientific studies to be associated with a multitude of health benefits, contains plentiful amounts of monounsaturated fat. Monounsaturated fat intake generally has no effect on total cholesterol level, and raises HDL cholesterol, a good fraction of cholesterol in the bloodstream. Until the early 1990s, many nutrition experts incorrectly (in retrospect) recommended significantly limiting intake of monounsaturated fat. (Historically, the basis of the outdated recommendation to limit monounsaturated fat intake was the focus of the neutral effect of monounsaturated fat on total blood cholesterol levels, with a lack of recognition that monounsaturated fat raises HDL cholesterol). Bottom line in 2024 is that plentiful consumption of monounsaturated fat is part of a healthy eating plan.

Polyunsaturated fat, as mentioned above, is essential in the diet, because the body is incapable of synthesizing omega 3 and omega 6 polyunsaturated fatty acids. The ‘old wisdom’ was to consume plentiful amounts of all polyunsaturated fat, based on data that intake of polyunsaturated fat lowers total cholesterol. The ‘new wisdom’ is to consume plentiful amounts of omega 3 polyunsaturated fat, but to limit intake of omega 6 polyunsaturated fat. Omega 3 fat in general has no effect on total cholesterol, but lowers blood triglyceride levels and raises HDL (good) cholesterol levels, whereas omega 6 fat in general has no effect on total cholesterol level but lowers HDL (good) cholesterol levels. Anthropological data would suggest that humans evolved on a diet in which the ratio of omega 6 to omega 3 fat was approximately 2:1. Published data indicates that the in the Standard American Diet (acronym SAD), the ratio of omega 6 to omega 3 fat is 20:1. While it considered "conventional wisdom" that a high omega 6: omega 3 ratio in the diet is pro-inflammatory, some nutrition experts assert that there is not data to support this assertion. There is a general consensus that arachidonic acid intake is pro-inflammatory, and thus that one should minimize intake of arachidonic acid.

Omega 3 fat is found in flax seeds/flax meal, walnuts, and oily fish, such as salmon, mackerel (canned, as king mackerel contains significant quantities of mercury), anchovies, sardines, and herring (acronym SMASH). Trout also contains plentiful quantities of omega 3 fatty acids. Tuna, king mackerel, and swordfish, while plentiful in omega 3 fatty acids should be consumed in limited quantities secondary to the high methylmercury content in these fish. It may be best to consume wild salmon (Alaskan salmon) rather than farmed salmon (Atlantic salmon) because the content of PCBs my be higher in farmed salmon - the scientific evidence is conflicting. For more detail on mercury content of various types of fish, go to my educational/informational web site, click on the page on ‘Nutrition’ and scroll down to the section on ‘fish.’ Omega 6 fat is present in corn oil, cottonseed oil, safflower seed oil, sunflower seed oil, sesame seed oil, and soy oil. All polyunsaturated fat, both omega 3 and omega 6, is biochemically unstable and subject to oxidation. Exposure to heat, light, or air accelerates this process of oxidation. For this reason, all polyunsaturated oils should be stored in the refrigerator and purchased in small containers (in any container of oil, as the oil is used up, the container fills with air, and the oxygen in air biochemically triggers oxidation). Ideally, all polyunsaturated oil should be purchased in darkened containers, as the penetration of light through the container during the time the oil is stored on the shelf prior to purchase is greater in a clear container. Flax oil may be especially biochemically unstable – if consumed, it should be purchased in a black container stored in the refrigerator in the store. Flax meal (stored in the freezer) may be more biochemically stable than flax oil. Ideally omega 3 fat intake should be 5-7% of total calories and omega 6 fat intake 7-10% of total calories. Bottom line in 2024 is that modest consumption of polyunsaturated fat is an important aspect of healthy eating; strive to achieve balance between omega 3 fat intake and omega 6 fat intake and to minimize consumption of foods with arachidonic acid.

Cholesterol is a fat-like substance present in animal products, and also synthesized in the human body. The ‘old wisdom’ was to limit consumption of cholesterol in the diet. This ‘old wisdom’ was based on a mistaken belief that dietary cholesterol intake raised blood cholesterol levels. The ‘new wisdom’ is that in most individuals, the dietary intake of cholesterol does not need to be restricted. While there does appear to be a small subset of the population in which dietary cholesterol intake does raise blood cholesterol levels (a small percentage of those individuals with a family history of very high cholesterol), emerging data indicates that in the vast majority of individuals, blood cholesterol level is determined primarily by genetics, the composition of fat intake in the diet, amount of exercise, and amount of stress, with minimal influence of dietary cholesterol intake on blood cholesterol level. In the 2015 Dietary Guidelines for Americans cholesterol is no longer listed as a "nutrient of concern."   Beware of deceptive labeling – by definition cholesterol is found only in animal products, so labels on oils or snack foods touting ‘NO CHOLESTEROL’ are deceiving, as by definition there cannot be any cholesterol in these products. The trans fat or omega 6 content of these ‘NO CHOLESTEROL’ products may nonetheless be detrimental to optimal human health. Also be aware that while cholesterol is ‘packaged’ in the blood into lipoproteins named HDL, LDL, and VLDL, there is only one type of cholesterol in food. Bottom line in 2024 is that modest consumption of cholesterol in foods such as eggs and shellfish is fine, except for those (a small minority of the population) with a genetic predisposition to very high blood cholesterol levels.

Carbohydrates: The ‘old wisdom’ was to limit intake of ‘simple carbohydrates,’ which are sugars, and consume plentiful amounts of ‘complex carbohydrates’ such as starch and fiber. Part of the ‘old wisdom’ was that plentiful intake of refined carbohydrates, such as white rice, pasta and bagels, was fine because these were ‘complex’ carbohydrates. The ‘new wisdom’ is that the glycemic index of the carbohydrates is very important, as high glycemic index carbohydrates raise blood sugar quickly, leading to a rapid rise in insulin level, followed by a drop in insulin level, and hunger.  It is believed that plentiful consumption of high glycemic index foods predisposes many individuals to obesity and diabetes. The shift in this country in the 1980s and 1990s from consumption of fatty foods to consumption of low fat foods with a high glycemic index likely contributed to the epidemics of obesity and diabetes.

 Glycemic index - one can think of the glycemic index as a measure of carbohydrate quality. Foods with a low glycemic index have less of an effect on blood sugar values and insulin levels in the blood than do high glycemic index foods. Part of the 'new wisdom' is that some ‘complex carbohydrates’ such as pretzels, bagels and some breakfast cereals have a glycemic index higher than that of table sugar! The ‘new wisdom’ is that the categorization of carbohydrates into simple and complex from a structural standpoint is meaningless from a ‘functional’ standpoint (functional referring to the hormonal effects of different types of carbohydrates). The glycemic index of a food is not shown on the label – one must consult glycemic index tables found in books or websites. In general, the higher the fiber content of a food, the lower the glycemic index. In general (corn and potatoes are exceptions) the glycemic index of vegetables is lower than the glycemic index of fruits.

Fiber is one type of carbohydrate – adequate fiber intake is very important. Fiber is categorized as (1) soluble fiber, which lowers cholesterol and increases satiety/fullness, and (2) insoluble fiber, which facilitates regular bowel movements, and may decrease the risk of colon cancer. By definition, fiber is distinguished from starch in that fiber is a component of cell walls in plants, whereas starch is a storage form of carbohydrate in plants. Starch is categorized as rapidly digestible starch, slowly digestible starch, or resistant starch, based on the amount of amylose versus amylopectin – glycemic index is highest for rapidly digestible starch, and lowest for resistant starch. Fiber intake in the diet ideally should be a minimum of 25-35 grams/day; intakes as high as 75-100 grams/day are probably ideal. Increase fiber intake gradually over time to minimize bloating and flatulence (gas). If one consumes cereals, a source of predominantly insoluble fiber, choose brands with at least 6 grams of fiber per serving. When one is reading the ‘Nutrition Facts’ on the cereal box label, along with a high fiber content, one should also look at the quantity of “Added sugars” (a new category, effective in 2021, on the ‘Nutrition Facts’ label on the container) and strive to purchase cereals with minimal added sugars.

Bottom line in 2024 as it pertains to carbohydrate consumption in the diet is to focus on eating high fiber foods and foods with resistant starch, and to minimize intake of processed foods, as these tend to have carbohydrate in a form which is metabolized in the body in a way which raises blood sugar too quickly and too much. In addition, if one is to eat a food with a high glycemic index (such as a banana, a piece of bread, a bowl of breakfast cereal), combine this food with other food which is rich in fats and/or protein (eggs, nuts, seeds, whole fat plain yogurt, fish, meat), as the fat/protein in the food slows the breakdown of carbohydrate in the body, minimizing a spike in blood sugar.

Protein: Whereas evidence-based scientific recommendations regarding the type and quantity of fat intake and the type and quantity of carbohydrate intake changed substantially in the 1990s, the scientific recommendations regarding the type and quantity of protein intake not change significantly until approximately 2020. Historically, for many decades, the recommended quantity of protein intake was 0.6 - 0.8 grams protein/kg body weight per day, for people of all ages. As per a review article (Malnutrition in Adults. N Engl J Med. 2024. 391. 155-165), while there is not complete scientific consensus in 2024, most experts now recommend intake of 0.8 - 1.2 grams protein/kg body weight per day, for healthy middle aged and older adults. Consumer Reports in 2024, based on emerging scientific consensus, suggests that seniors strive for intake of 1.2 grams protein/kg body weight per day.

There is ongoing (for decades) scientific debate about the relative benefits versus harms of soy consumption. The general consensus is that consumption of fermented soy foods is a healthy choice, and that moderate consumption of whole soy foods  is probably a healthy choice, but the health effects of consumption of isolated soy protein (i.e. soy burgers, soy cheese, soy hot dogs, soy bars) is incompletely understood. Historically soy was not consumed in concentrated form, and soy in supplements is in concentrated form.

Whereas animal protein is a high quality source of protein (it contains all 8 essential amino acids), the environment in which we live is such that environmental toxins are concentrated in animals at the top of the food chain, and often animal protein is ‘adulterated’ with hormones and antibiotics fed to the animals. Finally, unless one purchases grass-fed beef, the omega 3 to arachidonic acid ratio of the polyunsaturated fat in beef is not optimal, as most commercial beef comes from cows fed corn and soy (omega 6) rather than grazing on grass (a source of omega 3). Likewise, unless one purchase 'omega 3 eggs,' the omega 3 to arachidonic acid ratio of the polyunsaturated fat is not optimal. Fish are an excellent source of protein, along with the beneficial omega 3 fats found in oily fish, and legumes (beans, peas, lentils, soy) and nuts and seeds are excellent plant-based sources of protein. Nuts and seeds are also excellent sources of fiber and monounsaturated fat. Nuts and seeds are best kept in the refrigerator, to minimize oxidation of the monounsaturated fat in these foods.

The protein in the human body is composed of 20 biochemically distinct amino acids. Eight of the 20 amino acids in human protein cannot be synthesized by humans, and thus must be consumed in the diet – these are referred to as essential amino acids. The only substantial way in which the ‘wisdom’ on protein intake in the diet has shifted in recent decades is that historically it was believed that an individual needed to consume all 8 essential amino acids at every meal. Current 'wisdom' (for decades) is that it is sufficient to consume the 8 essential amino acids over the course of 24 hours, not necessarily at every meal. Since animal protein is ‘complete protein,’ meaning all 8 essential amino acids are present in ratios optimal to human health, whereas most plant protein is ‘incomplete,’ meaning that most plant sources of protein have suboptimal levels of one or more essential amino acids, the ‘new wisdom’ means that an individual who is not consuming animal product at a given meal need not be concerned about developing a deficiency of an essential amino acid, as long as that individual consumes a full complement of all 8 essential amino acids over the course of the day.

Bottom line in 2024 is that modest consumption of protein is a key component of a healthy eating plan (and based on the scientific recommendations shifting to a higher daily intake of protein, some middle aged adults and many seniors do not consume enough protein in the diet). Ideally most of the protein in the diet is consumed from plant sources, as plant-based protein may be healthier for the individual, and limitation of animal consumption at a global level will reduce global warming.

Books: Eat, Drink, and Be Healthy (2001) by Walter Willett, MD, DrPH is an excellent guide to optimum nutrition. The Anti-Inflammation Zone (2005) by Barry Sears, PhD is also a good guide to optimum nutrition. An excellent book with lots of information on the glycemic index is The New Glucose Revolution (1996) by Jennie Brand-Miller et al. The Omnivore's Dilemma (2006) by Michael Pollan thoroughly presents the health and environmental issues that are consequences of "factory farming."

Disclaimer: the preceding is intended as educational material and not as individual treatment recommendations.

Page Updated August 11, 2024