Research

Research:

Comparative Effects of Four Dietary Programs on Weight Loss and Coronary Risk Factors

Fleming, R.M. 2002. The effect of high-, moderate- and low-fat diets on weight loss and cardiovascular disease risk factors. Preventive Cardiology, 5 (3), 110-8.

Study. More than 60 percent of Americans are overweight, and a number of popular diets have been advocated, often without evidence, to alleviate this public health hazard. Cardiology specialists from the Fleming Heart & Health Institute in Omaha, Nebraska, investigated the effects of several diets on weight loss, serum lipids and other cardiovascular disease risk factors. For 1 year, the subjects (men and women) followed one of these four dietary programs: a moderate-fat program without calorie restriction (MF; 28 patients); a low-fat diet (Phase I; 16 patients); a moderate-fat, calorie- controlled diet (Phase II; 38 patients); and a high-fat diet (HF; 38 patients).

The MF program (2,000-2,200 calories per day [kcal/day]) was 20 to 30 percent (%) fat, 60% carbohydrate and 15% protein. The Phase I program (1,300-1,400 kcal/day), which consisted of fruits, vegetables and grains, was 10% fat, 75% carbohydrate and 15% protein. The Phase II program (1,500-1,600 kcal/day) was 15% fat (monounsaturated and polyunsaturated), 70% carbohydrate and 15% protein; this diet provided 350 to 500 fewer calories per day than were required to maintain body weight. The HF program (1,400-1,500 kcal/day) was 55%-65% fat, 10% carbohydrate (less than 100 grams per day) and 25%-30% protein.

Weight decrease was 2.6% (not significant [NS]) in MF patients, 18.4% (p = 0.045) in Phase I patients, 12.6% (p = 0.0085) in Phase II patients and 13.7% (p = 0.025) in HF patients.

Total cholesterol (TC) fell by 5% (NS) in the MF group, 39.1% (p = 0.0005) in the Phase I group and 30.4% (p = 0.0001) in the Phase II group; it increased by 4.3% (NS) in the HF group. LDL cholesterol (LDL-C) fell by 6.1% (NS) in the MF group, 52.0% (p = 0.0001) in the Phase I group and 38.8% (p = 0.0001) in the Phase II group; it increased by 6.0% (NS) in the HF group. There were nonsignificant reductions in HDL cholesterol (HDL-C) in the MF (-1.5%) and HF (-5.8%) groups. HDL-C levels increased by 9.0% (NS) in Phase I patients and 3.6% (NS) in Phase II patients.

Triglyceride (TG) levels increased in both the MF (1.0%) and HF (5.5%) groups, although neither increase was statistically significant. In people following the Phase I and II diets, TG levels fell by 37.3% and 36.9%, respectively. Homocysteine levels increased by 9.7% in the MF group and 12.4% in the HF group. Patients following the Phase I and II diets showed reductions of 13.6% and 14.6%, respectively. Only those following the Phase II diet showed a tendency toward significant improvement (p = 0.061).

Lipoprotein(a) [Lp(a)] levels increased by 4.7% (NS) in the MF group and 31.0% (NS) in the HF group; they fell by 7.4% (NS) in the Phase I group and 10.8% (NS) in the Phase II group. Fibrinogen levels increased only in subjects following the HF diet (11.9%), whereas patients following the MF, Phase I and Phase II diets showed nonsignificant reductions in fibrinogen (-0.6%, -11.0% and -6.3%, respectively).

Patients in the MF group demonstrated nonsignificant reductions in weight, LDL-C, TC, HDL-C, TC/HDL-C ratio and fibrinogen and nonsignificant increases in TGs, Lp(a) and homocysteine. There was significant weight loss in patients on the Phase I and II and HF diets after 1 year. Reductions in TC, LDL-C, TGs and TC/ HDL-C ratio were significant only in patients following either the Phase I or the Phase II diet. Only patients following the HF diet showed a worsening of each cardiovascular disease risk factor (LDL-C, TGs, TC, HDL-C, TC/HDL-C ratio, homocysteine, Lp(a) and fibrinogen)—this despite statistically significant weight loss.

Comments. This intriguing and well-controlled study is important because it illustrates the paradox of low-carbohydrate, high-fat diets (e.g., diets that allow unlimited meat and egg consumption). These programs clearly induce significant weight loss, often over just a few months, but cause significant increases in blood lipids and lipoproteins. Weight reduction should not be the only consideration when assessing dietary programs to improve health, especially in those prone to heart disease. Prospectively, either the Phase I or Phase II program coupled with an exercise program that expends about 1,500 kcal per week would be ideal for both weight loss and reduction of cardiovascular (and diabetes) risk factors.

Risk of Strenuous Exercise in Sedentary Men

Cadroy, Y., et al. 2002. Strenuous but not moderate exercise increases the thrombotic tendency in healthy sedentary male volunteers. Journal of Applied Physiology, 93, 829-33.

Study. Exercise scientists in Oslo, Norway, and Toulouse, France, collaborated to investigate the effect of moderate and strenuous exercise on experimental arterial thrombus formation in men. Thrombogenesis (the tendency to form blood clots, especially in the coronary arteries) was measured in 15 sedentary, healthy male volunteers at rest and immediately after two standardized 30-minute exercise tests. The tests were performed on a bicycle ergometer at a constant load corresponding to either 50% or 70% of maximal oxygen uptake (i.e., 65% or 80% of maximum heart rate). Thrombus formation was induced ex vivo by exposing a collagen-coated coverslip in a parallel plate perfusion chamber to native nonanticoagulated blood for 3 minutes (i.e., blood was drawn from the subjects during and immediately after exercise and then analyzed for thrombotic tendencies). Platelet and fibrin deposition was quantified by immunoenzymatic methods.

Moderate exercise did not affect arterial thrombus formation. In contrast, 30 minutes of exercise at 70% of maximal oxygen uptake increased platelet thrombus formation on collagen by an average of 20% (p = 0.03). Fibrin deposition on collagen remained unchanged with exercise, regardless of its intensity. Thus, according to the authors, the present study suggests that exercise of heavy intensity may increase the risk for arterial thrombogenesis in sedentary but healthy young males.

Comments. This study explicitly demonstrates why it is important to start previously sedentary individuals at low to moderate exercise intensities. This is especially true for previously sedentary individuals who have metabolic-syndrome-like risk factors (i.e., overweight, elevated blood pressure, elevated blood lipids). These individuals should also warm up by engaging in at least 10 to 12 minutes of graded aerobic exercise (e.g., walking at a modest pace or pedaling a stationary bicycle at a relatively low workload).

Stretching and Muscle Soreness

Herbert, R.D., & Gabriel, M. 2002. Effects of stretching before and after exercising on muscle soreness and risk of injury: systematic review. British Medical Journal, 325, 468-73.

Study. Researchers at the University of Sydney in New South Wales, Australia, evaluated the effects of stretching before and after exercising on postworkout muscle soreness, risk of injury and athletic performance. They reviewed eight controlled studies in the exercise science literature.

Five studies, all of moderate quality, reported sufficient data to be included in the analysis. Outcomes were very similar. Stretching produced small, statistically nonsignificant reductions in muscle soreness. The pooled estimate of reduction in muscle soreness 24 hours after exercising was only 0.9 millimeters (mm) on a 100 mm scale. Data from two studies on army recruits in military training showed that muscle stretching before exercising did not produce useful reductions in injury risk.

Herbert and Gabriel concluded that stretching before or after exercising does not confer protection from muscle soreness. They found that stretching before exercising does not seem to confer a practically useful reduction in the risk of injury but noted that the generality of this finding needs testing. They also concluded that insufficient research has been done to determine the effects of stretching on sports performance.

Comments. Notwithstanding the findings of this review, which are not dissimilar to those of other reviews on the efficacy of pre-exercise stretching, it should be said that pre-exercise stretching also serves as a psychological warm-up to physical activity and has been shown to lessen perceived fatigue in the early stages of an exercise session. Yoga poses that include significant muscle stretching have been found to improve muscular flexibility and joint range of motion, which clearly contributes to good musculoskeletal health.

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Ralph La Forge, MS

IDEA Author/Presenter
Ralph La Forge, MS, is a physiologist and board-certified clinical lipid specialist. He is the ma... more less
January 2003

© 2003 by IDEA Health & Fitness Inc. All rights reserved. Reproduction without permission is strictly prohibited.

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