Nutrients vs food choices of nutrients
Mary M. Fynn, Ph.D, RD, L.D.N
The objective of this article is to provide an introduction to the effects within the body of the different food sources of the nutrients. The standard way to teach nutrition is to discuss nutrients (protein, carbohydrate, lipids, etc.) and to discuss them as separate entities. However, we eat meals that are a mixture of foods and these foods nutrients; those that supply energy (carbohydrate, lipid and protein) and vitamins, minerals and phytonutrients. When we say a food is a “source” of a nutrient, we mean this nutrient is in high quantity relative to other nutrients in the food, or what is found in other foods. For example, bread is labeled a source of carbohydrate as it is mainly made from a grain; but bread also contains some protein and often a small amount of lipid. There are a variety of food choices for each nutrient and over time, the foods or food combination we select can impact our health. There is a growing literature that examines how the intake of specific foods, or form of the food, will either decrease or increase the risk of a chronic disease. Food can be used as medicine. Much of the information presented in this article synthesizes a number of articles/studies. There are some general references at the end should you want additional information.
The food groups for carbohydrate are starch, vegetables, fruit, and dairy. We also get carbohydrate from sweeteners, but “sweetener” is not a food group. Because so many foods contain carbohydrate, it represents at least 50% of the total calories in an average American diet. Sad to say, but surveys of the current American diet indicate the average American obtains close to half of their carbohydrate intake from sweeteners. Sweeteners in food have many names (sugar, fructose, rice syrup, high fructose corn syrup, etc.) but they are all carbohydrate devoid of nutritional benefits.
Health benefits of carbohydrate foods
Most of dietary carbohydrate is from plant products. All plant products contain phytonutrients, which are compounds that function in both the plant and in humans. In the plant, they protect the plant from the surrounding environment (UV rays, insecticides, pesticides, etc.); in humans, phytonutrients have been shown to have some amazing health benefits by improving risk factors for all chronic diseases. Phytonutrients are throughout the plant product but they tend to concentrate on the outside of the plant product, as they tend to function to protect the plant, and they increase with ripening and also when you ‘injure” the plant (e.g., cut, crush, ferment, etc.). When you eat the whole plant product or at least the outside of the plant product, you get more phytonutrients than when you just eat the inside (e.g., whole wheat flour v refined flour; berries v banana). The amount of phytonutrient that is absorbed into the body during digestion from the plant product will vary depending on a number of factors, such as the overall meal content, which can include inhibitors; what other components are present, etc. Most studies to date have indicated that the benefits of phytonutrients are from food and not from consuming the phytonutrients in isolation as a pill. Foods that contain a large number of different phyonutrients and have been related to improving risk factors/ decreasing the risk of chronic diseases are called “functional foods” and include foods like extra virgin olive oil (the juice of the olive fruit), tomatoes, grapes as a fruit, and more so when they are used to produce wine.
Starch is the storage form of carbohydrate in plants and is made up of complex carbohydrate, which is a chain of glucose units. Starch foods are mainly composed of carbohydrate but they also contain some protein and often small amounts of lipid. Refined grains contain just the endosperm of the grain which is somewhat nutrient poor, while whole grain also contains the bran and the germ. Whole grain is a source of insoluble fiber and contains more lipid than refined as it has the germ intact. Whole grain also contains phytonutrients, and trace minerals like selenium, iron, zinc, magnesium and copper. Whole grain also naturally contains a number of B vitamins, some of which are added back to refined flour. Whole grain intake is related to lower body weight and less weight gain over time (1); a decrease in the risk of cardiovascular disease (2, 3); and a decrease in several cancers (primarily those of the gi tract) (4). Legumes (beans) are a source of starch that contains both insoluble and soluble fiber and phytonutrients.
Vegetables and fruit are mainly carbohydrate; vegetables also have some protein. Only a vegetables and fruits contain lipid few (avocado, olives). Vegetables are simple carbohydrate when they are first formed but mature to more complex carbohydrate. As simple carbohydrate tastes sweeter on the tongue, this is why “young” vegetables taste sweeter than older ones. The carbohydrate in fruit is also simple carbohydrate, but it is initially more complex carbohydrate, which is why ripe fruit tastes sweeter than when it is first formed.
Vegetables and fruits, in general, have long been recommended for health improvement. However, some have greater health benefits than others and the literature more supports vegetables improving health, especially cancer protection, than fruit. Two phytonutrient families that have consistently been shown to have cancer protection are the carotenoids and the glucosinolates. Carotenoids give color to plant products and the deeper the color, the higher the carotenoid content. Deeper color comes from longer time on the plant before harvesting than what is grown to be sold as “retail fresh”; for this reason, I recommend the use of frozen and canned produce as they are kept longer on the plant than what is typically sold as retain fresh (excluding local/ seasonal produce). Frozen and canned produce have comparable nutrient content to retail fresh versions (5) and there are studies indicating that the frozen/ canned versions have greater content and bioavailability of carotenoids and other phytonutrients (6). There are hundreds of carotenoids and their role in cancer protection has been fairly well studied (7). The glucosinolates are in the cruciferous/ cabbage family vegetables (broccoli, Brussel sprouts, cabbage, cauliflower, collard greens, kale) and they provide cancer protection (8), and seem to be especially powerful for decreasing both breast and prostate cancer risk (9). The absorption of both carotenoids and the glucosinolates is enhanced, and possibly dependent on dietary fat, which is addressed in the lipid section.
Dairy products contain the simple carbohydrate lactose, which is a disaccharide of glucose + galactose. Dairy products contain sufficient protein to also be classified as a protein food. The lipid content of dairy is based on weight and can be quite high, as in whipping cream (35% or 35 grams per 100 g) to non-fat milk, which is also called “skim” as all the fat is skimmed off the milk (and used to make full-fat dairy products like cream, cheese, and ice cream).
When we eat a food containing carbohydrate, the monosaccharides (glucose, fructose, galactose) are absorbed into the portal system. The liver converts the majority of the fuctose and galactose to glucose so the carbohydrate seen in the blood is primarily glucose. Glucose can be used right away for energy or stored as glycogen on the liver, which is used to maintain blood glucose, and in muscles with this glycogen used only by the muscle in which it is stored. Glycogen storage is limited so any excess carbohydrate consumed will be converted to fatty acids and stored in the adipose tissue.
High fructose corn syrup (HFCS) is an inexpensive sweetener. The per capita consumption in the US was 0.6 lb in 1975 and peaked at 63 lbs in 2000; in 2007 it was 56 lbs. The use of HFCS has generated a fair amount of press due to the potential health concerns. Excessive consumption (which has not been defined) leads to higher blood levels of fructose as the liver seems to be limited in the amount of fructose that can be converted to glucose. Fructose does not stimulate insulin secretion, and fructose can enter cells without insulin; in the cell, fructose is catabolized to trioses which are use to make fatty acids; so fructose is a carbohydrate not stored as glycogen. The conversion of fructose to triose units instead of storage as glycogen is how fructose intake is hypothesized to contribute to obesity.
Diets proportionally high in carbohydrate and lower in fat will lead to higher fasting blood levels of glucose and insulin compared to diets more moderate in carbohydrate and fat; for a person with excessive fat storage (i.e., overfat) a high carbohydrate diet can produce large increases in fasting blood glucose and insulin, likely aggravated by underlying insulin resistance. Higher levels of both glucose and insulin, including those in the “normal” range, have been related to an increase risk of heart disease (atherosclerosis) (10, 11), and several cancers, including breast (12, 13) and prostate (14, 15).
Lipids can be liquid, which are commonly called “oils” or solid, which are commonly called “fats”. The lipid that provides energy is the triglyceride, which contains 3 fatty acids. The fatty acids can be saturated (or no double bonds), or unsaturated, with at least 1 double bond, with the monounsaturated fatty acids [MUFA] having 1 double bond and polyunsaturated [PUFA] having 2 or more. Saturated fats “pack well” so they are solid at room temperature; double bonds make kinks in the fatty acid chain which results in a more fluid or liquid product. The 3 fatty acids on a triglyceride are a mixture of saturated and unsaturated fatty acids and are named by which type predominates (i.e, there is no triglyceride that is contains only 1 type of fatty acid). Animal fats are higher in saturated fat; the only rich sources of saturated fat in the plant kingdom are the tropical oils, palm and coconut. The high saturated fat content is useful in the tropical oils as they have a higher ambient temperature in the tropics. Vegetable oils are high in MUFA and PUFA; olive oil contains the highest amount of MUFA; extra virgin olive oil is the product closest to the olive as it is the juice of the olive; refined olive oil is lower quality oil and does not have health benefits. Extra virgin olive oil has been related to decreasing both heart disease (16) and a number of cancers (17). Canola oil is also high in MUFA; it was first introduced in the mid-1980’s when it was realized that olive oil had health benefits. It was erroneously thought that the MUFA content of olive oil was the source of the health benefits so canola oil was developed from the rapeseed plant. Unlike olive oil, canola oil has not been shown to have health benefits.
Vegetable seed oils are high in PUFA; due to the double bonds, vegetable oils are more liquid than olive oil or canola oil. The main vegetable oil in the US is soybean; others are safflower and corn oil. Fish oil is also primarily PUFA, but fish oil lipid is longer chain PUFA (20 carbons are greater) than the PUFA in vegetable oils. All polyunsaturated fats readily oxidize.
Tree nuts are primarily a lipid food but they also contain a fair amount of protein. Nut consumption of about 5 oz/week has been shown to significantly decrease heart disease risk (18, 19). Despite being somewhat high in calories, frequent nut consumption has been inversely related to body weight (20) and significantly less weight gain over time compared to those who never or seldom ate nuts (21).
The two essential fatty acid families are omega 3 and omega 6; they are “essential” because humans cannot put a double bond in a fatty acid before the 9th omega carbon (i.e., we can make oleic acid). The 18 carbon starting member (i.e., the other members are made from these) in the omega families are: linolenic acid for omega 3 and linoleic acid for omega 6. Both omega families make eicosanoids (the hormone-like compounds that regulate a variety of bodily functions) from the 20 carbon members. In general, the eicosanoids made by the omega 3 family decrease risk factors for heart disease and some cancers. However, it is the ratio in the blood of the 2 families that have been related to lower rates of disease/ better health as there is competition at the first enzyme in eicosanoid production so whichever family predominates will determine which eicosanoids are made. Humans can make arachidonic acid (20 carbon omega 6 fatty acid) from linoleic acid but we can not efficiently elongate/ desaturate linolenic acid (18:3) to make EPA and DHA (22, 23). Thus, plant sources of omega 3 (nuts, vegetables oils, flaxseed) will not provide the health benefits associated with omega 3 fatty acids. The major source of omega 6 is vegetable seed oils (18 carbon linoleic is primarily found in soybean, safflower, corn) and red meat (the major source of arachidonic acid in the American diet). Thus the American diet is high in omega 6, due to the use of vegetable oils and red meat, and the typical American blood ratio is about 1 omega 3: 17 to 20 of omega 6; while the healthiest ratio is not known, ratios with proportionally more omega 3 long chain fatty been related to less chronic diseases. Fish oil pills are widely used / recommended to improve the ratio but decreasing or eliminating vegetable oils and/or red meat will also improve the ratio. It should be kept in mind that both families are polyunsaturated fats so they will both oxidize.
When we eat foods that contain lipid, the constituent fatty acids are incorporated into chylomicrons which can then distribute where we have fatty acids in our body (lipoproteins, cell membranes, phospholipids). Lipids are typically discussed in how they affect the lipoproteins; however, their effect is dependent on the antecedent diet or the comparison diet. As a general statement, SFA increase levels of both LDL and HDL. However, not all food sources of SFA increase CHD risk. Red meat, mainly as beef, has been related to an increased risk of CHD (24), while most studies indicate that dairy products, including cheese and butter, are not related to CHD risk or may decrease risk (25). Monounsaturated fat can decrease LDL relative to SFA and either increase or not change HDL (extra virgin olive oil has been shown to independently increase HDL but canola oil does not, so changes in HDL are dependent of the source of MFA); PUFA decrease LDL more than MFA, which is why they are favored in lipid lowering diets, but they will also oxidize the LDL particle and it is oxidized LDL that is taken up by the scavenger pathways and leads to atherosclerosis. Although PUFA containing oils are recommended in the US for cardiovascular health (26), it has been known for close to 20 years that the adipose content of linoleic acid is positively related to the degree of coronary disease (27).
Low-fat, higher carbohydrate diets have been recommended in the past for decreasing LDL levels. As low fat diets are typically higher in carbohydrate, the effect of low-fat diets is to raise VLDL/ fasting triglyceride levels (you can not store all the glucose as glycogen so the extra glucose is converted to fatty acids → triglycerides) (28). There can either be larger VLDL particles or more VLDL particles, but the result is less VLDL is converted to LDL [lipoprotein metabolism review: the VLDL particle made by the liver to carry endogenous triglyceride circulates in the body and has the triglyceride content removed by lipoprotein lipase mainly at the site of the adipose. When sufficient triglyceride has been removed, you have an LDL particle]. So low-fat diets can lower LDL, but at the expense of increasing triglycerides. As there is an inverse relationship between triglycerides and HDL, low-fat diets also lower HDL.
There are some dietary benefits to including fat in a meal. Fat in a meal contributes to satiety or the feeling that helps you to stop eating; fat in a meal will also delay the time until you get hungry. Lipid digestion causes the release of gastric inhibitory peptide (GIP), which slows gastric emptying; lipid digestion also causes the release of cholecystokinin (CCK); besides its role in lipid digestion, increasing blood levels of CCK contribute to satiety.
Dietary fat can also provide health benefits. Dietary fat is needed to absorb the fat soluble vitamins (ADEK), carotenoids (29) and possibly the glucosinolates, which are water soluble and lost in preparation with water (30). The necessity of dietary fat to absorb carotenoids probably explains why studies assessing intake of dark vegetables indicate limited to no health benefits, which studies of blood levels of carotenoids are related to decreasing cancers (7). Eating dark produce or cruciferous vegetables without fat means you get little to none of the phytonutrients into your body. In addition, fat (and extra virgin olive oil in particular) make vegetables taste better. Compared to a lower fat diet, a diet containing olive oil may mean a higher intake of vegetables (31).
Dietary protein is digested and absorbed as individual constituent amino acids. Plant sources of protein are called I”ncomplete” as they are lacking one or more essential amino acid (except soy and quinoa) but it is quite easy to obtain sufficient protein from a vegetable based diet. Vegetarian and even vegan diets supply sufficient protein and have been related to healthier body weight (32) and better overall health (33) compared to diets that frequently include meat.
Protein has been the nutrient with somewhat of a star status for a number of years. Protein has a number of important body functions; however, it is quite easy to meet protein needs by diet and supplements are not necessary. There are several points to keep in mind when discussing protein:
We can get all the vitamins and minerals we need with a varied diet. It is not necessary to take a supplement, even a multivitamin. I find that many patients use multivitamin as “health insurance” as in: “I don’t always eat that well, but I do take my multivitamin”. My advice is to eat a diet that contains a variety of foods and skip the vitamin pills. No supplement will improve your health; that is the role of the phytonutrients, which are only found in plant foods. The larger concern with supplements is toxicity. Many of the toxicity symptoms mimic common aches and pains so they may go unrecognized. The supplement industry is poorly regulated due to Dietary Supplement Health and Education Act (DSHEA) which was passed in 1994. This act basically unregulated the supplement industry as it reclassified supplements as food so they are no longer regulated by the FDA as a food additive or drug, but now fall under the jurisdiction of the USDA. Supplement manufacturers do not need to prove the safety of the product; the FDA would need to prove a supplement as unsafe. Also, due to vitamin and mineral enrichment/ fortification of foods, especially breakfast cereals/bars, the additional use of supplements, including multivitamins, increase the likelihood of toxicities.
The fat soluble vitamins are A, D, E, and K. As they are fat soluble, they are digested and absorbed with dietary lipid and carried in the chylomicron. Vitamin A is found naturally only in liver, fatty fish, eggs and is fortified into milk, so it is not easy to get sufficient vitamin A in the diet. However, several of the carotenoids are classified as “provitamin A” as they can be converted to vitamin A so eating dark produce will provide carotenoids for vitamin A synthesis. Frozen/ canned produce are especially dark in color as they are kept on the plant until fully ripened. Vitamin A is also in many multivitamins and added to many breakfast cereals/bars. Excess intake of vitamin A from supplements and fortified foods has been related to hip fractures in post menopausal women (36-38).
Vitamin D is found naturally in fatty fish (fish oils) and added to some breakfast cereals/ bars; it is difficult to get sufficient vitamin D from food. Vitamin D is classified as a “pro-hormone” as we could in theory make all we need in our skin via ultraviolet radiation striking the skin. However, due to concerns of excessive sun exposure and decrease time spent outdoors by young folk, the vitamin D deficiency diseases of rickets (growing people) and osteomalcia (adults) are increasing in prevalence. Vitamin D (D3) in a pill form is needed for those who are deficient as you cannot get enough vitamin D in the diet.
There are 8 forms of vitamin E and they each have different functions. Several forms of vitamin E are found in oils. Vitamin E as alpha tocopherol is the fat soluble antioxidant. Interestingly, the requirement for vitamin E as the fat soluble antioxidant assumes one is regularly consuming polyunsaturated fats (vegetable oils), which will oxidize. Alpha tocopherol is found primarily in extra virgin olive oil which conveniently does not readily oxidize as it is primarily monounsaturated fat. Thus, the vitamin E in vegetable seed oils functions mainly to keep the oil from oxidizing (rancid) while the vitamin E in olive oil can be used as an antioxidant in our body.
Vitamin K functions primarily in clotting; however, it also has a role in bone strength (37). Leafy green vegetables (spinach, collard greens, kale, broccoli rabe) are rich sources of vitamin K. Leafy greens also contain the B vitamin folate and a number of phytonutrients; leafy green intake has been inversely related to a number of cancers. With Coumadin use, vitamin K intake needs to be considered as vitamin K will counteract the blood thinning effect of Coumadin. The options are to recommend the patient not consume leafy greens or that they consume leafy greens consistently and the Coumadin dose be adjusted to account for the vitamin K in their diet. The latter option may take a few more visits to adjust the Coumadin required, but it will also improve the patient’s long term health. Interestingly, Coumadin use for greater than one year has been shown to be an independent predictor of both spine and hip fracture (37).
The water soluble vitamins are all the B’s and vitamin C. Many of the B vitamins function in metabolism as coenzymes as they are needed for the release of energy from nutrients and the formation of ATP. From this comes the erroneous notion that taking B vitamins will provide energy (as in taking them when one is tired). The metabolic cycles are dependent on the energy yielding nutrients (carbohydrate, lipid, protein) for energy extraction and trapping; taking B vitamins does not lead to more cycling and energy trapping. The American diet contains plenty of B vitamins and several of the more important ones are added to flour. The only B vitamin of potential concern is B12 as it requires several proteins to digest and absorb it from food so there is the potential for genetic defect(s) that would result in B12 not being absorbed from the diet. Also, B12 is only found in foods of animal origin so vegans can be at risk of deficiency. Vitamin B12 supplementation typically bypasses the gi (injection or nasal gel) due to the number of proteins needed for B 12 absorption.
Vitamin C is probably the most widely used (abused?) vitamin. It has a role in immunity but there is no evidence that supplementation will decrease cold frequency, length of stay or severity, despite attempts to prove this is so. These studies might be the clearest example of the placebo effect as many show that those with any benefit were with participants who thought they were receiving vitamin C. Colds are also hard to study; when did it start? end? what is “severe” (very subjective)? A concern with vitamin C supplements is the dose. Vitamin C is maximally absorbed at about 125 mg; larger doses will not be readily absorbed so water will be brought into the gi leading to loose stools/ diarrhea (which may be attributed to the cold and not the excessive vitamin).
Minerals are divided into major and trace, depending on the requirement. Minerals are not easy to absorb and one needs to consider bioavailability when discussing minerals. Bioavailability is: the degree to which the amount of the ingested mineral is absorbed and available to the body. Absorption rates vary from a low of 1 to 2% to at most 50 to 60%. This means that if you look at the nutrient composition of a food and see what amount of a mineral is in the food, you will only absorb a fraction of the amount in the food. This is a good thing as all of the minerals have toxicities which can mimic other illness symptoms. One of the main determinants of absorption is current need for the nutrient: if you are deficient in the mineral, you will absorb more if it; if you have sufficient stores, the mineral is not absorbed. Some of the factors that affect bioavailability:
Phytonutrients: while mainly providing wonderful health benefits, some can interfere with mineral absorption. For example”
Mineral to mineral interaction:
Due to similar valences, calcium, iron, magnesium and copper will all compete for absorption and it would be difficult (impossible?) to determine which is being absorbed if they are all present; this is thought to be an issue mainly with supplements and not food as food sources of these nutrients tend to better distribute in the chyme.
Vitamin-to- mineral interaction: