Clinical Abstracts
With Comments from Adriane Fugh-Berman, MD
Low-calorie Entrees Decrease Total Calorie Intake
June 1999; Volume 1: 55
Source: Rolls BJ, et al. Energy density but not fat content of foods affected energy intake in lean and obese women. Am J Clin Nutr 1999;69: 863-871.
Design and Setting: A within-subjects study of women who consumed meals in the laboratory for four test periods of four days each.
Subjects: 34 women (17 lean, 17 obese), aged 18-45.
Treatment: Food representing half of each subject’s usual energy intake was manipulated either for energy density or fat density. Besides the "compulsory entrees," volunteers could eat whatever else they wanted. The amount of this self-selected food was monitored.
Outcome Measures: Intake of self-selected foods.
Results: In both lean and obese subjects, consumption of low-energy density foods reduced intake of self-selected foods at meals by 16%. Fat content did not significantly affect energy intake. Palatability of diets was comparable and ratings of hunger did not differ between diets.
Funding: NIH grants DK-39177 and DK-08926 and the International Life Sciences Institute Foundation. General Mills, Inc. conducted fiber analyses of foods and Quidel donated OvuQuick kits used in the study.
Comments: Energy density means calories. Essentially, this study manipulated entrees for both fat and calories, and found that eating foods high in fiber and moisture but low in calories reduced subjects’ appetites. Calories were lowered by utilizing foods containing more water and fiber. So, the low-fat, low-calorie entree utilized more fruit and vegetables; the low-fat, high-calorie entree utilized more pasta, rice, and bread, and the high-fat, high-calorie entree utilized more butter, oil, and full-fat products. Fat promotes satiety, but eating a high-fat entree clearly did not reduce subjects’ appetite for side dishes.
It is very interesting that only manipulating half of the usual caloric intake resulted in significantly decreased total intake. This could have implications for dieters. Eating low-calorie entrees (without limiting side dishes) may seem less daunting to dieters than trying to eat low-calorie everything all the time. Entrees based on fruits or vegetables appear to be filling, reduce the intake of other foods and have other health benefits as well.
Incorporating Exercise into Daily Life May Be as Good as Going to the Gym
June 1999; Volume 1: 55-56
Source: Andersen RE, et al. Effects of lifestyle activity vs. structured aerobic exercise in obese women: A randomized trial. JAMA 1999;281:335-340.
Design and Setting: 16-week randomized controlled trial with one-year follow-up. Study was conducted in a university-based weight management program.
Subjects: 40 obese women, aged 21-60.
Treatment: Low-fat diet (1,200 kcal/d) and either a structured aerobic exercise program (three step aerobics classes weekly) or moderate lifestyle activity (increasing physical activity for 30 minutes a day on most days by walking short distances, taking stairs instead of elevators, etc.).
Outcome Measures: Changes in body weight, body composition, cardiovascular risk factors, and physical fitness.
Results: Both groups lost weight (8.3 kg in the aerobic group and 7.9 kg in the lifestyle group), with no significant difference between the groups. Serum triglyceride levels and total cholesterol levels decreased significantly in both groups with no significant differences between groups. The aerobic group lost less fat free mass. At one-year follow-up, the aerobic group regained 1.6 kg while the lifestyle group regained 0.08 kg.
Funding: National Research service award NF32DK09241-01 and NIH Research Scientist Development Award K02-MH00702-08.
Comments: Making time to go to the gym can be difficult for many people, and may be particularly daunting for those who are obese. It is heartening to learn that merely walking more and using stairs more may result in positive changes in terms of weight loss, body composition, and lipids. It bears noting that this level of weight loss—and weight loss maintenance—is far superior to that attained with weight loss drugs as well. However, it is impossible to separate out the effects of exercise on these variables in this study because everyone consumed a low-calorie diet. It would have been preferable to include a third arm in this study looking at the effects of low-fat diet alone without changes in exercise.
Type and Amount of Fat Associated with Breast Cancer Risk
June 1999; Volume 1: 56
Source: Holmes MD, et al. Association of dietary intake of fat and fatty acids with risk of breast cancer. JAMA 1999;281:914-920.
Objective: To determine whether total intake of fat or intake of fatty acids are associated with breast cancer.
Setting/Methods/Subjects: The Nurses Health Study, a cohort study of 88,795 U.S. women who are sent detailed health and diet questionnaires every two years. The study began in 1976; this report is a 14-year follow-up of those women who answered the 1980 diet questionnaire and who did not have diagnosed cancer (other than non-melanoma skin cancer) prior to 1980.
Results: 2,956 women were diagnosed with breast cancer during this period. Compared to women eating 30-35% fat, women who consumed less than 20% of their calories from fat did not have a lower incidence of breast cancer than those who ate higher amounts. The incidence of breast cancer was slightly higher in women who consumed less than 30% of calories from fat. No increased risk was found for increased intake of animal fat, polyunsaturated fat, saturated fat, or trans-unsaturated fats (in models in which fat intake replaced carbohydrate intake). In general, increased intake of vegetable oils or monounsaturated fat also didn't make a difference. Women who consumed the most omega-3 fats from fish had a slightly increased risk of breast cancer.
Funding: NIH grant CA40356. Additional funding for individual authors from Harvard Center for Cancer Prevention and the 50th Anniversary Program for Scholars in Medicine.
Comments: This study found no increased risk of breast cancer with increased intake of any fat or fatty acid (with the surprising exception of omega-3 fatty acids from fish). Even women who consumed more than 50% of their calories from fat were not at increased risk. These data were analyzed in a number of different ways, quite thoroughly. For example, breast cancer risk factors were examined in order to ensure that a low-fat diet was not a marker for elevated risk. (In other words, if women who knew that they were at elevated risk of breast cancer deliberately altered their diets, then more high-risk women would show up in the low-fat group. This was not the case).
This study is particularly interesting given that epidemiologically, populations that consume very low-fat diets have a lower rate of breast cancer incidence; additionally, animal experiments show a lower rate of mammary tumors with diets that contain under 20% fat.
The number of women eating a diet under 20% fat was relatively small (20 cases of breast cancer/6,539 person-years) but probably accurately reflects the percentage of the general U.S. population consuming this type of diet, which is quite stringent.
The Nurses Health Study is a large observational study that has provided many interesting findings over the years. However, observational trials can provide only evidence, not proof. That will have to await the results of the Women's Health Initiative, a large-scale, randomized controlled trial. While the main purpose of the trial is to examine the effect of hormone replacement therapy vs. placebo on a variety of health outcomes, there is also a low-fat diet arm to this trial. Results, however, will not be available until about 2007.
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