What clinicians need to know about diets for their patients

Physicians should collaborate with patients, set obtainable goals.

Providing dietary counseling for cardiovascular risk prevention is challenging. Thousands of books, leaflets, and articles have been written on weight loss, sending mixed messages to our patients.

However, despite the many articles in the popular press about the epidemic of obesity and the importance of healthy living and fitness, we as a society are becoming increasingly obese and unfit. In fact, nearly one in three Americans is now considered to be obese.

Roger S. Blumenthal

Over the last decades, there have been numerous studies that have attempted to discover the “holy grail” of dietary success. Although there has been no absolute path that works for everyone, we have made some progress, and it is important to be cognizant of the most recent updates in dietary health so that we can best serve our patients.

Traditionally, low-fat diets decreased saturated fat intake to improve cardiovascular status. However, these low-fat diets often shifted energy sources to refined carbohydrates and added sugars that increased rates of obesity, insulin resistance, and diabetes. High-fat/low-carbohydrate diets, such as the Atkins diet, were then popularized. Many health experts remain concerned about the negative long-term implications of these diets with respect to renal and hepatic complications, as well as the potential for increased atherogenesis.

A new generation of diets, focusing on low animal fat content and increased portions of protein, fiber, fruits, and vegetables, have become more pervasive. Carbohydrates are now differentiated based on the degree of glucose surge after their consumption, also known as the glycemic index. With high-glycemic index foods, there is increased insulin release which heightens the risk of obesity and insulin resistance. Some of these diets with a low glycemic index include the South Beach Diet, Sugar Busters, and the Zone Diet. The DASH and Mediterranean diets have a similar macronutrient formula.

Recent evidence

In the last few years, several trials have been released that have contributed greatly to our understanding of the issue.

Beulens and colleagues investigated the impact of dietary glycemic index and glycemic load (glycemic index x carbohydrate content) on the risk of CVD in 15,704 Dutch women with no diabetes and without known coronary disease. They were aged 49 to 70. There were about nine years of follow-up. They discovered that high dietary glycemic load (HR=1.47, P=.03) and glycemic index (HR=1.33, P=.02) increased the risk of CVD, particularly for women with a BMI >25 (for glycemic load, HR=1.78, P=.04).

In the A to Z Weight Loss Study, Gardner and colleagues studied four weight-loss diets of varying carbohydrate intake in 311 overweight premenopausal women without diabetes who received two months of diet and weekly instruction followed by 10 months of follow-up. In this trial, those women on the Atkins diet with the lowest carbohydrate intake lost more weight and had more favorable metabolic effects at 12 months than did women assigned to the other three diets. Weight loss with the diets included Atkins 4.7 kg, Zone 1.6 kg, LEARN 2.6 kg, and Ornish 2.2 kg. Weight loss was not significantly different among the women on the non-Atkins diets, while weight loss with the Atkins diet was significantly greater than weight loss with the Zone diet (P<.05).

Halton and colleagues studied 82,802 women in the Nurses’ Health Study. These women completed a questionnaire used to calculate a low-carbohydrate-diet score (percentage of carbohydrates vs. protein and fat). Comparisons were then made between the highest and lowest deciles and this was then correlated with the risk of CHD. During 20 years of follow-up, diets higher in protein and fat were not associated with an increased risk of CHD. However, when the fat and protein come from vegetable sources, these diets may actually reduce the risk of CHD (RR=0.70, P=.002). Further, their data suggest that a higher glycemic load was strongly associated with an increased risk of CHD (RR=1.90, P=.003).

Ebbeling and colleagues compared a low glycemic load (40% carbohydrate and 35% fat) vs. low-fat diet (55% carbohydrate and 20% fat) on body weight and cardiovascular risk factors in 73 obese young adults, and clinical outcomes were assessed for 18 months. Insulin levels were recorded 30 minutes after administration of a glucose load. In those participants with insulin levels higher than the median, a low-glycemic load diet led to 5.8 lb weight loss while the low-fat diet led to a weight loss of 1.2 kg (P=.004). Body fat percentage was also favorably affected in these same participants with respect to a reduction in body fat. A low-glycemic load was associated with a 2.6% reduction in body fat while the low-fat diet led to a reduction in body fat percentage of only 0.9%. This trial demonstrated that reducing glycemic load may be especially important in achieving weight loss in individuals with high insulin secretion and that a low glycemic diet resulted in more favorable HDL and triglyceride profiles.

MacMillan-Price and colleagues studied impact of glycemic load in 129 overweight young adults via four different low-fat diets with different protein and carbohydrate composition. This study found that both high-protein and low glycemic index regimens increased body fat loss. Women on low carbohydrate/high-glycemic index diets and high carbohydrate/low-glycemic index diets lost 80% more fat mass (4.6 kg and 4.5 kg) than did those on high carbohydrate/high-glycemic index diets (2.5 kg; P=.007). Cardiovascular risk reduction was optimized by a high-carbohydrate/low-glycemic index diet as LDL levels fell by 6.6 mg/dL in the women following a high carbohydrate/low-glycemic index diet while they rose by 10 mg/dL in the low carbohydrate/high glycemic index diet women (P=.02).

Howard and colleagues randomized and studied 48,835 postmenopausal women in the Women’s Health Initiative Dietary Modification Trial over eight years. They showed that an intervention reducing total fat intake and increasing amounts of vegetables, fruits, and grains did not significantly reduce the risk of CHD, stroke or CVD, although there was a trend towards benefit with respect to CHD. Modest effects were found on CVD risk factors. However, we must keep in mind that the trial was designed to focus on lowering rates of breast and colorectal cancer, not CVD. Intake of polyunsaturated fat, fiber, fruits, vegetables and other macronutrients were lower than current recommendations, and it is highly possible that the currently recommended diet would have achieved greater cardiovascular benefit in this study.

In early 2005, Dansinger and colleagues published a comparison of the Atkins, Ornish, Weight Watchers, and Zone Diets in 160 overweight adults with known hypertension, dyslipidemia or fasting hyperglycemia, with one year of follow-up. In this study, each diet modestly reduced body weight and levels of several cardiac risk factors. Most importantly, increased adherence to any of the diets was associated with greater weight loss and risk factor reduction.

How to advise patients

In synthesizing these trials, it is clear that there is no perfect dietary program for everyone. However, there does seem to be a general dietary strategy. A diet low in animal saturated fat and high in plant proteins and polyunsaturated fats, fruits, vegetables, grains, and fiber is optimal. Further, minimizing high-glycemic index carbohydrates is likely beneficial, and these positive effects may be more pronounced in those who are obese and insulin resistant.

However, we must remember that the approach to weight loss and improved cardiovascular health should be multi-pronged. Below is a simple ABCDE approach that can be emphasized during counseling and selection of a dietary strategy:

• A: Adherence. Adhering to a sustained and effective dietary regimen is necessary for long-term success. Physicians should encourage a family member of the patient to attend clinic visits; another “set of ears” is helpful, and family members can facilitate compliance.
• B: Bottom Line. Realistic weight loss objectives, with input from patients, should be measurable and agreed upon at the office visit. Concrete goals will lead to greater effort and accountability.
• C: Clarity and Collaboration. Dietary recommendations must be explained clearly. Information sheets can be tailored to the patient’s educational level. Those with the capacity to understand may appreciate reading more about the science of dietary therapy while those less inclined would benefit more from simply stated dietary lists. Providing recommendations of particular nutritionists may also be helpful. A collaborative approach often will be most successful.
• D: Diet. A diet must be selected that seems most consistent with the eating preferences of the individual. Choice is good, and patient and family input is important.
• E: Exercise. Exercise is equally important as dietary intake. In addition to burning calories, it has cardioprotective effects on lipid levels and endothelial function. Pedometers are an inexpensive tool that can be used to encourage activity. To achieve desired fitness levels, walking more than 10,000 steps a day or engaging in brisk exercise for 60 minutes or more each day is recommended. Some physician offices are able to establish discounted membership fees for their patients at local fitness facilities.

Conclusion

Healthy dietary habits are at the core of preventing CVD. Although there is no clear dietary recipe for weight loss and optimal cardiovascular health, recent studies have suggested that minimizing animal saturated fats and high-glycemic index carbohydrates, while focusing on increasing plant protein and fats, grains, fiber, fruits, and vegetables, will likely improve health while promoting weight loss. In attempting to establish a dietary regimen, success will be more likely if the physician collaborates with patients, sets obtainable objectives, educates patients and their families, and encourages patients to take ownership of their health.

For more information:

• Beulens JWJ, de Gruijne LM, Stolk RP, et al. High dietary glycemic load and glycemic index increase risk of cardiovascular disease among middle-aged women. JACC. 2007;50:14-21.
• Gardner CD, Kiazand A, Alhassan S, et al. Comparison of the Atkins, Zone, Ornish, and LEARN diets for change in weight and related risk factors among overweight premenopausal women. The A to Z Weight Loss Study. JAMA. 2007;297:969-977.
• Halton TL, Willett WC, Lue S, et al. Low-carbohydrate-diet score and the risk of coronary heart disease in women. N Engl J Med. 2006;355:1991-2002.
• Ebbeling CB, Leidig MM, Feldman, HA, et al. Effects of low-glycemic load vs. low-fat diet in obese young adults. JAMA. 2007;297:2092-2102.
• Dansinger ML, Gleason JA, Griffith JL, et al. Comparison of the Atkins, Ornish, Weight Watchers, and Zone diets for weight loss and heart disease risk reduction. JAMA. 2005;293:43-53.
• McMillan-Price J, Petocz P, Atkinson F, et al. Comparison of four diets of varying glycemic load on weight loss and cardiovascular risk reduction in overweight and obese young adults. Arch Intern Med. 2006;166:1466-1475.
• Howard Bv, Van Horn, L, Hsia J, et al. Low-fat dietary pattern and risk of cardiovascular disease. JAMA. 2006;295:655-666.
• Hu FB. Diet and Cardiovascular disease prevention. JACC. 2007;50:22-24.
• Parikh P, McDaniel MC, Ashen MD, et al. Diets and cardiovascular disease – An evidence-based assessment. JACC. 2005; 45:1379-1387.