continued
In a two-year study, 171 women on a low-fat diet achieved a maximum weight loss of only about seven and a half pounds at 6 months, and by year two some of that weight was regained. Most significantly, the standard deviation was more than twice the average weight loss, showing that a number of subjects actually gained weight on the low-fat diet, not counting the 13 that dropped out of the program. (Sheppard L et. al. Weight Loss In Women Participating in a Randomized Trial of Low-Fat Diets. American Journal of Clinical Nutrition 1991;54:821-8.).
As astonishing as this may sound, it's in no way surprising to those who've spent time reviewing the peer-reviewed scientific literature. The truth is that not one clinical study has ever shown that low-fat diets allow long-term reversal of obesity in most subjects, whether combined with exercise or not. Perhaps most damning of all, according to the USDA, Americans' fat consumption has consistently gone down over the last 20 or so years while the American national rates of obesity have gone up at precisely the same time. Correlation is not causation, but it is hard to jibe this fact with claims that lowering fat intake helps those who are overweight to reduce their body fat, or the widespread claim that lowering fat intake makes it possible to eat more food without gaining weight. Some explanations have been offered to continue to support the low-fat paradigm as a workable weight-loss diet, but none are very compelling and none have strong clinical support.
"In the adult US population the prevalence of overweight rose from 25.4% from 1976 to 1980 to 33.3% from 1988 to 1991, a 31% increase. During the same period, average fat intake, adjusted for total calories, dropped from 41.0% to 36.6%, an 11% decrease. Average total daily calorie intake also tended to decrease, from 1,854 kcal to 1,785 kcal (-4%). Men and women had similar trends. Concurrently, there was a dramatic rise in the percentage of the US population consuming low-calorie products, from 19% of the population in 1978 to 76% in 1991. From 1986 to 1991 the prevalence of sedentary lifestyle represented almost 60% of the US population, with no change over time...Reduced fat and calorie intake and frequent use of low-calorie food products have been associated with a paradoxical increase in the prevalence of obesity." (Heini AF; Weinsier RL. Divergent trends in obesity and fat intake patterns: the American paradox.) American Journal of Medicine, 1997 Mar, 102(3):259-64)
(Note: I'm interested in hearing about any scientific literature which DOES support the low-fat diet as an effective weight-loss diet; if you have any please email me at my first name (dean) at my deanesmay.com domain.
Low-fat diets are dangerous
Not only is there reason to question the belief that low-fat diets improve health or give significant help in weight loss efforts, but there is a growing amount of evidence that such diets are actually quite unhealthy, raising the risk of heart disease, diabetes, and cancer, not to mention certain psychiatric disorders such as depression and schizophrenia.
A recent American study showed that low-fat, high-carbohydrate diets (15% protein, 60% carbohydrate, 25% fat) increase risk of heart disease in post-menopausal women over a higher fat, lower carbohydrate diet (15% protein, 40% carbohydrate, 45% fat). (Jeppeson, J., et. al. Effects of low-fat, high-carbohydrate diets on risk factors for ischemic heart disease in postmenopausal women. American Journal of Clinical Nutrition, 1997;65:1027-33)
The largest and most comprehensive study on diet and breast cancer to date, studying over 5,000 women between 1991 and 1994, showed that women with the lowest intake of dietary fat had a significantly higher incidence of breast cancer than the women with the highest intake of dietary fat. It also found that women with the highest intake of starch had a significantly higher incidence of breast cancer than the women with the lowest intake of starch. The study found no evidence that saturated fat had any effect one way or the other on breast cancer, and that unsaturated fat had a significantly protective effect against breast cancer. (Franceschi S et. al. Intake of macronutrients and risk of breast cancer. Lancet; 347(9012):1351-6 1996)
A study involving tens of thousands of American women showed that diets high in carbohydrate (which almost all low-fat diets are) significantly raise women's risk of developing diabetes, although cereal fibre intake seems to have a limited protective effect. (Jorge Salmeron et. al. Dietary Fiber, Glycemic Load, and Risk of Non-insulin-dependent Diabetes Mellitus in Women. Journal of the American Medical Association. 1997;277:472-477)
High intake of fats from the Omega-3 group increase HDL cholesterol, which is considered protective against heart disease. Obviously it would be difficult to eat an Omega-3 rich diet while following a traditional fat reduced diet, especially if one were following one of the popular American diets that has one eating only 20-30 grams of fat per day. (Franceschini G. et. al. Omega-3 fatty acids selectively raise high-density lipoprotein 2 levels in healthy volunteers. Metabolism, 1991 Dec, 40:12, 1283-6. See also Journal of the American College of Nutrition 1991:10(6);593-601)
A strong correlation exists between schizophrenia and deficiencies in fats, especially in the n-3 series. Schizophrenics who naturally eat lots of Omega-3 fats tend to have less severe symptoms than those who don't. Supplementation with extra fats in the Omega-3 group significantly improves symptoms of schizophrenia in most patients. Close relatives of schizophrenics show similar deficiencies in Omega-3 fats. The possibility that diets generally low in fat might worsen schizophrenia or even bring on the condition among those already predisposed to it is hard to ignore. (Laugharne JD; Mellor JE; Peet M. Fatty acids and schizophrenia. Lipids, 1996 Mar, 31 Suppl:, S163-5. See also Peet M et. al. Essential fatty acid deficiency in erythrocyte membranes from chronic schizophrenic patients, and the clinical effects of dietary supplementation. Prostaglandins Leukot Essent Fatty Acids, 1996 Aug, 55:1-2, 71-5)
"Our results do not support the recommendation of an isoenergetic high carbohydrate, low fat diet for improving peripheral insulin action in adults with glucose intolerance ... the increase in insulin action that we observed previously with vigorous exercise training was negated when combined with a diet high in carbohydrates and fiber. ... The subjects in this study are at increased risk for developing NIDDM." (American Journal of Clinical Nutrition 1995;62:426-33) [note: NIDDM is Non-Insulin Dependent Diabetes Mellitus -- the most common form of diabetes.]
Low-fat high-carbohydrate diets eaten by patients with diabetes (NIDDM) have been shown to lead to higher day-long plasma glucose, insulin, triglycerides, and VLDL-TG, among other negative effects. In general, study has demonstrated that multiple risk factors for coronary heart disease are worsened for diabetics who consume the low-fat, high-carbohydrate diet so often recommended to reduce these risks. (Chen YD et. al. Why do low-fat high-carbohydrate diets accentuate postprandial lipemia in patients with NIDDM? Diabetes Care, 1995 Jan, 18:1, 10-6)
"Conventional wisdom holds that low fat diets improve insulin sensitivity. Unfortunately, this is true only after an ultra-low carbohydrate diet. No changes in glucose tolerance and substrate oxidation were measured after a high-carbohydrate low fat diet. In addition, these studies confirm a growing body of evidence that increasing dietary carbohydrate increases plasma triglycerides and decreases plasma high-density-lipoprotein (HDL), increasing the risk of cardiovascular disease." (Metabolism 1993:42:365-70)
Numerous studies have shown that high-carbohydrate low-fat diets lead to high triglycerides, elevated serum insulin levels, lower HDL cholesterol levels, and other factors known to raise the risk of coronary artery disease. (See Liu GC; Coulston AM; Reaven GM. Effect of high-carbohydrate low-fat diets on plasma glucose, insulin and lipid responses in hypertriglyceridemic humans. Metabolism, 1983 Aug, 32:8, 750-3. See also Coulston AM; Liu GC; Reaven GM. Plasma glucose, insulin and lipid responses to high-carbohydrate low-fat diets in normal humans. Metabolism, 1983 Jan, 32:1, 52-6. See also Olefsky JM; Crapo P; Reaven GM. Postprandial plasma triglyceride and cholesterol responses to a low-fat meal. American Journal of Clinical Nutrition, 1976 May, 29:5, 535-9. See also Ginsberg H et. al. Induction of hypertriglyceridemia by a low-fat diet. Journal of Clin Endocrinol Metab, 1976 Apr, 42:4, 729-35)
Is That All?
The references given above do not represent all the evidence against the low-fat diet as a worthless, possibly dangerous, diet. They represent merely a sampling of some of the more relevent studies. Below is some recommended reading for those interested in learning more on the subject.
The simple fact of the matter is that the low-fat diet is a fad diet. Warnings about the dangers of fat in the diet are constant in the media. Fat-phobia is ubiquitous among health-conscious Americans, and a surprising number of people from all walks of life (including most health professionals) continue to recommend a low-fat diet and to preach the "dangers" of fat. Such messages often take on an almost hysterical, or even belligerant, tone. Yet a growing mound of scientific data not only suggests that this diet fad is pointless, but suggests that it may actually be dangerous to the health of millions of Americans and others worldwide.