J Clin Gastroenterol. 2015 Sep;49(8):633-7.

Diet, Obesity, and Political Involvement


Robert M. Craig, M. D.

Emeritus Professor, Northwestern University Feinberg School of Medicine

1025 Terrace Court, Lake Geneva, WI 53147

Telephone and e-mail. 312-664- 3324, r-craig@northwestern.edu



This essay is an opinion article addressed to the busy practitioner. It provides information on nutrition, diet, nutritional science, and obesity to serve as a reference in teaching his patients on these issues. It is composed by a gastroenterologist who has been engaged in clinical gastroenterology and nutrition, research, and teaching in an academic medical center for 35 years. It also relates the information to conclusions on reasonable involvement of the national government in these topics. Finally, its audience might include the interested, well-educated, lay public. Hence, excessive scientific parlance and referencing have been avoided.

PMID: 26106846


Supplemental Material

Obesity is discussed as a major health problem for developed countries. It contributes to type 2 diabetes mellitus, arteriosclerosis (including stroke and coronary artery disease), musculoskeletal disorders, the metabolic syndrome, some cancers, and diminished mobility in the elderly and in those with musculoskeletal problems. Many measures have been advocated to address the problem, including specific diets, exercise programs, dietary medications, and vitamins. In spite of these efforts, there has been little impact on the problem.


The nature, physiology, and biochemistry of humans are addressed. Along these lines, concepts of adaptability and interchange among the nutrients are discussed in terms of specific food nutrients. An understanding of the categories of nutrients is necessary to grasp concepts of energy balance and obesity.   There are finely tuned mechanisms involving the gastrointestinal tract, the kidneys, the blood, the tissues, and the membranes of cells, assuring homeostasis. The three nutrients that contribute to energy balance are proteins, carbohydrates, and lipids (fats). All of our bodily functions are dependent upon proteins. Carbohydrates and lipids provide energy for the functioning of the body, including maintenance of heat, movement, and the cellular chemical processes involved in homeostasis, and there is interchangeability among them. Excessive ingestion leads to storage as fat. Digested proteins also enter the intermediary metabolic cycles as their constituent amino acids and can produce energy or be synthesized into carbohydrates (gluconeogenesis) or fats and excess proteins are also stored as fat.


Although these three moieties have specialized uses, their essential functions, which cannot be performed by the other two, they are exchangeable from the standpoint of energy production and fat storage. However, the amounts of energy generation from the three are not identical. Fats are much more energy dense than the other two. Ingestion of fat promotes much more fat storage, when excessive, than equivalent amounts of proteins or carbohydrates. The need to store metabolic fuel is determined by the metabolic rate of the organism. If fuel intake exceeds output, storage of fat eventuates. The metabolic rate is comprised of the basal energy expenditure and the energy required for any additional physical work (exercise). The amount stored as fat is increased with less exercise.


There are significant genetic determinations of obesity, including eating habits; higher metabolic rates in thin individuals exposed to over feeding; biologic twin observational studies; and information on leptin, a satiety hormonal factor, ghrelin, a hunger stimulating factor, and the hypothalamus.


A daunting task has been the development of recommended dietary allowances (RDAs) for micronutrients, the amount that prevents a deficiency disease for each nutrient. One approach to this has utilized blood levels for a micronutrient, relating this to some effect on the body. One can screen a large, healthy, population and find the average and variance of the micronutrient, then compare this to a group that has some defect, presumably due to a diminished store of the micronutrient. Then a difficult translation to the amount of the micronutrient required to promote restitution of the blood level would be required.


Gluten is a general term for some of the proteins found in wheat, barley, and rye, and is responsible for celiac disease (CD), a relatively common malady, affecting around 1% of those of northern European ancestry. Our most common gastrointestinal disturbance is the irritable bowel syndrome (IBS), which may have the same symptoms as celiac disease. However, most patients with IBS do not have celiac disease. Current investigations are underway to see if a subgroup of IBS patients is intolerant to gluten containing diets, without having CD. Many who have promulgated avoidance of gluten for a host of different symptoms with little or no evidence supporting the contentions have expanded this information. There are food intolerances in normal individuals, often more prominent in those with IBS. Many of these are idiosyncratic, and do not lend themselves to general therapeutic dicta. Although food allergy has been suggested as being responsible for these intolerances, classic allergic mechanisms, presenting clinically with a skin rash or trouble breathing, are relatively uncommon.


The best type of investigation is a randomized, doubly blind trial to see if an intervention is therapeutically useful for a disease. Some studies of specific nutrients have been performed to see if the nutrient has a salutary role. Experimental studies have suggested that vitamins with anti-oxidant properties, such as vitamin A or vitamin E, might have a binding effect on free radicals, or reactive oxygen species, and might prevent or reverse cancer. Unfortunately, well controlled randomized, double blind studies have not shown efficacy.


In looking at more complex problems, such as obesity, one can see other confounding influences. If a trial of a high fat vs. a low fat containing diet is entertained, various things need to be “controlled” to exclude their influence: the other components of the diets, for example protein content, should be equivalent; there has to be assurance that the diets are rigorously followed; a decision has to be made whether to keep the caloric content the same or to allow the subject to eat as much as he wants of the diet; the amount of physical exercise must be the same for each group; the two groups must be as close to identical as possible, usually achieved statistically by randomization; and the duration of the study should be long enough to achieve meaningful results. Many of these characteristics cannot be achieved in the outpatient setting, and, yet, it is outpatients who will be taking the advice derived from the studies. Most weight loss studies comparing various diets have not controlled for calories and have shown efficacy in the short-term, but not the long term. This should not surprise us, as weight loss or gain is related to total calories ingested, not to the type of food (fat, carbohydrate or protein), due to the caloric interchangeability of these nutrients; and to the amount of physical exercise performed.


Some have advocated avoidance of sweet foods in children as they might condition children to eat less “nutritionally rich” foods. Note that exclusion of fruits is not included in the proscription, even though many are quite sweet. One can see the difficulties in doing a well-controlled study of this thesis, randomizing one group of children to have no artificial sweeteners and no sweetened beverages (except “natural” fruit juices), the other with no restrictions, for a prolonged duration, perhaps a year, and measuring the effect on body-mass-index (a measurement of body fat content). The most important chore would be the exclusion of sweetened beverages in our society and the onerous task of supervising the restrictions. Those of us with children and grandchildren understand the difficulties.


Concluding comments: First, It should not be surprising that specific diets to control, modify, or prevent obesity have not shown efficacy over simple caloric restriction. Gustatory satisfaction is one of the pleasures of life, and many of our social engagements take place around food and liquid consumption. Programs to modify this behavior will usually fail, especially in the long run. Governmental programs trying to force dietary changes, when there is no strong, scientific evidence supporting the measures, is an un-wise restriction of liberty. Various dietary programs should undergo the same scientific evaluation that other treatment programs undergo.


Secondly, obesity should be considered a characteristic, similar to other differences among members of our species (height, skin color, eye color, intelligence, sociability, etc.) and should not be an object of scornful criticism.


Third, the most effective strategy for weight control is to effect change on the other side of the metabolic equation, exercise. Weight gain is directly related to caloric input and inversely related to metabolic activity and exercise.


Fourth, it is reasonable for governmental involvement in labeling contents of food that would specify harmful ingredients for specific diseases, such as gluten for celiac disease and phenylalanine for phenylketonuria. In addition, it is reasonable to indicate the caloric content of foods, as the information might influence one’s behavior in weight control programs. Further, listing Na and K content of foods might assist consumers with heart and kidney disorders. The cost involved in labeling all of the micronutrients for each food item, both for the manufacturer and the monitoring, and, eventually, to the consumer seems excessive. Further, governmental labeling of “nutritious foods,” vs. “non-nutritious foods” is not well supported by well-performed, scientific, studies. No food is intrinsically “unhealthy” for the general population, but its healthiness is dependent upon a point of view. Someone subject to heart failure or with failing kidneys might require salt restriction, whereas Na restriction for the general population might be harmful. Listing some carbohydrates as “healthy” (those in fruit juices) whereas others (fructose in cola products) as “unhealthy,” does not make sense as each carbohydrate eventuates in the same metabolic cycles within the liver, and are metabolically interchangeable.


Fifth, the FDA does a responsible assessment of drugs, and should be the judge of the safety of artificial sweeteners, vitamin and megavitamin use, along with its consideration of other drugs.



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