Diet - Optimum Nutrition
Nutrition is complicated, and there is no way to make it simple! I believe, as do many other 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 better 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 carbohydrate upon insulin levels. Additionally, the ratio of omega 3 to arachidonic acid fat content of the diet is important because of the hormonal effect of these fats on eicosanoid hormone levels in the body. The concepts 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.
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 must be consumed in the diet. Fat as a general entity is neither good nor bad – one must examine each type of fat separately. Remember, nutrition is not simple!
There is universal agreement amongst nutrition experts that trans fat intake is bad. Trans fat intake not only raises the blood cholesterol level, but also lowers the HDL cholesterol, the good fraction of cholesterol in the blood. Trans fat is fat which has 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 awareness of the ill health effects of trans fat, there is an ongoing concerted effort by manufacturers of food to eliminate trans fats from food. As of 1/1/06, 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.
There is some 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, dairy is worst, meat less bad, tropical oils even less bad, and chocolate 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. Spingolipids 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.
Monounsaturated fat, found 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, is plentiful in 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).
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 ground flax seeds (i.e. flax meal), walnuts, and oily fish, such as salmon, sardines, tuna, mackerel, and trout. Due to the polluted environment in which we live, it is best to consume wild salmon (Alaskan salmon) rather than farmed salmon (Atlantic salmon) because of the higher content of PCBs in most farmed salmon. In addition, it is best to restrict consumption of white tuna and king mackerel because of the high methylmercury content in these fish. For more detail on mercury content of various types of fish, go to my educational/informational web site, and go to the outline 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 in ‘food containers’ 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). 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 seems to 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.
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 (i.e. markedly limit intake of eggs). This ‘old wisdom’ was based on a mistaken belief that dietary cholesterol intake raised blood cholesterol levels. The ‘new wisdom’ is that intake of 1-2 eggs per day is acceptable. While there does appear to be a small subset of the population in which dietary cholesterol intake does raise blood cholesterol levels (a few 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 note that while cholesterol is ‘packaged’ in the blood into lipoproteins named HDL, LDL, and VLDL, there is only one type of cholesterol in the diet.
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 a high glycemic index diet predisposes many individuals to obesity and diabetes. The shift in this country over the past couple of decades from consumption of fatty foods to consumption of low fat foods with a high glycemic index likely has contributed to the epidemic 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 decreases the risk of constipation, 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 for subsequent use as fuel/food for the plant. 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 should be at least 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 for a moderate to low sugar content, ideally less than 12 grams of sugar per serving.
Protein: Whereas the ‘wisdom’ regarding fats and carbohydrates has changed substantially over the past decade, the ‘wisdom’ regarding protein has not changed significantly. There continues to be debate as to the role of high protein diets with regard to achievement and maintenance of weight loss in the long term. There also continues to be 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 never consumed in concentrated form, as in supplements.
Whereas animal protein is a high quality source of protein, the environment in which we live is such that environmental toxins are concentrated in animals at the top of the food chain, and much 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.
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' 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.
Books: Eat, Drink, and Be Healthy (2001) by Walter Willett is an excellent guide to optimum nutrition. Dr. Willett, mentioned in the first paragraph of this article, is a MD who also has a doctorate of public health, and he is chairman of the Nutrition Department at the Harvard School of Public Health. 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 a consequence of "factory farming."
Disclaimer: the preceding is intended as educational material and not as individual treatment recommendations.
Page Updated June 14, 2018