The Not So Great Fat Debate

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Back in March 2010, meta-analysis concluded data from 21 epidemiological studies did not support a causal relationship between saturated fat intake and cardiovascular disease (CVD). The results of this study were quickly dismissed as proof only that epidemiological studies often fail to find real causal connections because they use seriously flawed methods of assessing dietary intake. Never- theless this flawed analysis led to the American Dietetic Association (ADA) to put together a panel of experts to debate whether or not Americans should be told to reduce dietary fat to help prevent obesity, type 2 diabetes, CVD, and cancer. The edited transcripts of this debate appeared in the May 2011 issue of the Journal of the American Dietetic Association. There did not appear to be much of a debate except perhaps for one panelist (Mozaffarian) who claimed replacing saturated fat with carbohydrate would adversely impact blood lipids and increase CVD risk. Dr. Lewis Kuller quickly debunked this naive claim. There seemed to be a consensus that total or % dietary fat was unrelated to CVD, cancer, diabetes or obesity but that the type of fat was import with all panelists agreeing that reducing saturated fat and trans and replacing it with more essential fatty acids (omega-3 & 6) would improve blood lipids and lower CVD risk. The panelists were less enthusiastic about replacing saturated fat with carbohydrate and monounsaturated fat although all acknowledged - except Dr. Mozaffarian - that this would also lower LDL-cholesterol and likely help reduce CVD as well.

Certainly none of the advocates of a low-fat diet have suggested they be replaced refined carbohydrates to aid weight loss and reduce the risk of CVD, cancer and diabetes. Creating a position no one really advocates and then attacking this phony posi- tion is known as a “red herring.” Advocates of low-fat diets such as the Pritikin Longevity Center have always advocated not only reducing fat and particularly fatty animal products (except fish) but also largely eliminating refined carbohydrate. Very-low-fat, near vegetarian (VLFNV) diets composed largely of whole fruits, vegetables and grains have been shown to dramatically lower LDL- cholesterol levels and improve nearly all proven and suspected CVD risk factors. More important- ly a VLFNV diet has been shown to dramatically reduce angina, the need for heart surgery, and to dramatically reduce total mor- tality in patients with advanced coronary artery disease. Indeed, a VLFNV diet approach has been shown to shrink atherosclerotic plaques and significantly im- proves blood flow to the heart, while comparable data support- ing the use of higher “good” fat diets does not exist.

None of the panelists thought advice to lower total fat intake or % fat intake would aid weight loss. Indeed, Dr. Willett from Harvard even stated “...if anything the literature is showing slight advantages toward the higher-fat diet.” Of course, Dr. Willett and the other panelists are basing this on clinical trials that did not come close to achieving a healthy low-fat diet of the kind recommended by Pritikin or Ornish. One can hardly conclude anything from such poorly conducted studies except perhaps that compliance with a low-fat diet is difficult to achieve over the long term in free living subjects. By contrast, data from controlled clinical trials sug- gests reducing fat certainly can help people lose weight while limiting the hunger typically seen on calorie restricted diets that limits there long term efficacy. When fat intake was reduced by replacing high fat foods like whole milk with low-fat milk and adding less fat to recipes for things like muffins Dr. Lissner demonstrated a marked reduction in ad libitum calorie intake. On the lowest fat diet (<20% fat calories) subjects consumed 658 fewer calories per day than on the highest fat diet (>45% fat calories). Today we now know that this spontaneous reduction in calorie intake when dietary fat is reduced is largely due to the reduction in energy density. More recently, at Penn State a one- year study of 97 obese women looked at the impact of dietary counseling to reduce dietary fat alone or in conjunction with advice to also increase fruit and vegetable intake. Those that were only advised to reduce fat intake lost and kept of 14lbs after one year. Those counseled to also increased fruit and vegetable intake lost and kept off 17lbs. The authors conclude: “Reducing di- etary energy density, particularly by increasing fruit and vegetable intakes with decreased fat intake, is an effective dietary strategy for managing body weight while controlling hunger.”

Bottom Line:

ADA’s “Great Fat Debate” appears to have not been much of debate and some of its conclusions are lacking credible scientific support.

By James J. Kenney, PhD, RD, FACN.

References: 1. Am J Clin Nutr 2010;91:535-46 2. Clin Appl Nutr 1992;2:81-93 3. Am J Clin Nutr 1987;46:886-92 4. Am J Clin Nutr 2007;85:1465-77

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