Are We Getting Nutrition All Wrong?
What if everything you knew about nutrition was wrong?
Posted Nov 19, 2010
What if saturated fats weren't bad for you? What if obesity wasn't caused by sedentary behavior and overeating? What if exercising and eating less weren't the solution to losing weight? What if everything you have been told about nutrition was wrong?
This is the provocative thesis of Gary Taubes' book Good Calories, Bad Calories (1). One by one Mr. Taubes dispels nearly every belief doctors and the public health community hold to be true about nutrition and health - from how blood cholesterol and dietary fat aren't risk factors for cardiovascular disease to how the benefits of exercise and salt reduction have been overstated. It would be easy to dismiss his claims, except that he makes his case not with theories and conjectures, but through a meticulous review of the nutrition and medical literature going back a hundred years.
In debunking our current ideas about health and nutrition, Good Calories, Bad Calories puts forth a theory of its own - that carbohydrates, and in particular refined carbohydrates, are the dietary cause of chronic disease. It is the starches, processed grains, and sugars that are to blame for our current epidemics of obesity, diabetes, coronary heart disease, and even cancer.
To say that, if true, Mr. Taubes' ideas would transform the practice of preventive health and nutrition would be a gross understatement. They would literally change the face of nutrition as we know it. No more "fat-free" foods. No more meat is bad for you. No more calorie-restricted diets. No more turbo-charged exercise programs. Instead, the focus would be on eliminating refined carbohydrates: soda pop and sweetened drinks; pastas, breads, and cereals; and starchy vegetables such as potatoes. The perfect diet would basically follow this recipe (2):
"Foods to be avoided:
1. Bread and everything else made with flour
2. Cereals, including breakfast cereal and milk puddings
3. Potatoes and all other white root vegetables
4. Foods containing much sugar
5. All sweets
You can eat as much as you like of the following foods:
1. Meat, fish, birds
2. All green vegetables
3. Eggs, dried or fresh
5. Fruit, if unsweetened or sweetened with saccharin, except bananas and grapes"
Contrast this to the latest USDA guidelines (3):
- "Consume a variety of nutrient-dense foods and beverages within and among the basic food groups while choosing foods that limit the intake of saturated and trans fats, cholesterol, added sugars, salt, and alcohol.
- Consume less than 10 percent of calories from saturated fatty acids and less than 300 mg/day of cholesterol, and keep trans fatty acid consumption as low as possible.
- Keep total fat intake between 20 to 35 percent of calories, with most fats coming from sources of polyunsaturated and monounsaturated fatty acids, such as fish, nuts, and vegetable oils.
- When selecting and preparing meat, poultry, dry beans, and milk or milk products, make choices that are lean, low-fat, or fat-free.
- Limit intake of fats and oils high in saturated and/or trans fatty acids, and choose products low in such fats and oils.
- Choose fiber-rich fruits, vegetables, and whole grains often."
As I read Good Calories, Bad Calories one thing that kept bothering me was how the public health community could be so wrong. If the carbohydrate-insulin hypothesis is true, and the dietary fat-cholesterol hypothesis wrong, how could our nation's leading scientists, doctors and public health experts miss it? Mr. Taubes' explanation is that we have been practicing bad science. Instead of letting experimental observations speak for themselves, we have let our expectations and preconceptions bias us. When a study shows that eating less saturated fat does not improve health, we conclude that the study is flawed or "not sufficiently powered" to detect the benefit. When our obese patients tell us that they are cutting back on calories and trimming down the fat yet are not losing weight, we assume that there aren't be wholly truthful or are not exercising enough. Furthermore, we aren't subjecting many of our beliefs about nutrition (which really are hypotheses) to rigorous scientific testing. We have assumed that because fat in the blood is bad for our health that eating more fat must also be bad, and that because change in weight equals calories in minus calories out that consuming more calories or burning less calories must cause obesity.
As someone interested in preventive health, as a physician, and simply as a person who wants to remain healthy; I have had a hard time reconciling the conventional thinking with Mr. Taubes' conclusions. On one hand, it seems that nearly the entire public health community agrees that dietary fat is bad and that obesity is caused by overeating. These ideas are treated as dogma and serve as the foundation for an entire public health infrastructure aimed at combating chronic disease. In the face of such overwhelming agreement, who am I, or Gary Taubes for that matter, to disagree? On the other hand, there is something about the truth that, well, just rings true. To me, Good Calories, Bad Calories has that quality, because it helps explain many everyday conundrums. It explains why so many overweight people eat less than their lower weight peers but continue to be overweight, why we are seeing an explosion in diabetes and obesity despite exercising more and eating less meat than we did 100 years ago, and why obesity and chronic disease disproportionately strike lower income groups. It also puts forth ideas that make sense biologically. Because we evolved under conditions in which we had no access to processed carbohydrates, we are poorly adapted to our current environments, in which processed sugars account for an ever increasing proportion of our diets.
What I find most convincing is evidence in the standard medical literature that supports of Gary Taubes' conclusions. A recent meta-analysis of over 500 prospective cohort studies and randomized clinical trials published in a major academic journal found "insufficient evidence" that intake of dietary fat, excluding trans fat, is associated with coronary heart disease. (4) At the same time, it found "strong evidence" that foods with a high glycemic index or load are harmful for coronary heart disease. The authors write (and this is worth reading verbatim):
"The general consensus from the evidence currently available is that a reduced consumption of saturated and trans-fatty acids and a higher intake of fruits and vegetables, polyunsaturated fatty acids including omega-3 fatty acids, and whole grains are likely beneficial. This is reflected in the revised Dietary Guidelines for Americans 2005 from the US Departments of Health and Human Services and Agriculture. However, little direct evidence from [randomized clinical trials] RCTs supports these recommendations. [emphasis is mine] In some cases, RCTs have not been conducted, and RCTs that have been conducted have generally not been adequately powered or have evaluated surrogate end points rather than clinical outcomes. Despite this lack of information, evidence-based recommendations derived from cohort studies have been advocated. This is cause for concern because dietary advice to limit the intake of a certain nutrient (ie, dietary fat) may result in increased consumption of another (ie, carbohydrates), which can have adverse effects on CHD risk factors. Moreover, without large prospective studies in which multiple health outcomes are evaluated, recommendations to modify a dietary component may decrease the likelihood of one chronic disease (ie, CHD) at the cost of increasing another (ie, cancer)."
We've been told for years that the American "meat and potatoes" diet is what's killing us. But now an increasingly vocal group of experts is suggesting that it isn't the meat but rather the potatoes that are doing us harm. In the end, I'm not sure what the right answer is, but what I do know is that the chance that we are getting nutrition wrong is too important for us to ignore.
Copyright Shantanu Nundy, M.D.
(1) Good Calories, Bad Calories: Challenging the Conventional Wisdom on Diet, Weight Control, and Disease by Gary Taubes (published 2007, ISBN 978-1400040780).
(2) From reference 1, Page xiii. Originally from The Practice of Endocrinology by Greene et al 1951.
(3) These are a subset of recommendations from the Executive Summary of Dietary Guidelines for Americans 2005, accessible at http://www.health.gov/dietaryguidelines/dga2005/document/html/executives....
(4) Mente A, de Koning L, Shannon HS, Anand SS. A systematic review of the evidence supporting a causal link between dietary factors and coronary heart disease. Arch Intern Med. 2009 Apr 13;169(7):659-69. http://archinte.ama-assn.org/cgi/content/full/169/7/659.