In Search of the Healthy Diet
Abstract & Commentary
By Joseph E. Scherger, MD, MPH, Clinical Professor, University of California, San Diego. Dr. Scherger reports no financial relationships to this field of study.
Synopsis: Three diets were studied replacing saturated fats with 1) a carbohydrate-rich diet, 2) a protein-rich diet, and 3) a diet rich in unsaturated fat (predominately monounsaturated fat). All 3 diets lowered blood pressure, improved serum lipids and reduced calculated coronary heart disease risk. Diets rich in protein or unsaturated fat were better than the high carbohydrate diet in the overall calculations, although the protein rich diet resulted in lower HDL
Source: Appel LJ, et al. Effects of protein, monounsaturated fat, and carbohydrate intake on blood pressure and serum lipids: results of the OmniHeart randomized trial. JAMA. 2005;294:2455-2464.
This study was conducted by the omniheart collaborative Research Group based at Johns Hopkins University. This group followed up on the research which led to the Dietary Approaches to Stop Hypertension (DASH diet), which is now widely used for the dietary prevention and treatment of hypertension.1 The 3 diets studied were modifications of the DASH diet, varying the amount of carbohydrate, protein and unsaturated fat.
This OmniHeart Trial used a crossover design with 164 individuals with either prehypertension or stage 1 hypertension. The study participants consisted of 45% women, 55% African Americans, and 79% were overweight or obese. The basic DASH diet was modified to contain 58% carbohydrate, 25% protein (half from plant sources) or 37% unsaturated fat intake using olive oil, canola oil, safflower oil, nuts, and seeds. Each diet was ingested for 6 weeks and was designed to keep weight constant.
All 3 diets resulted in a modest drop (2-4 mm Hg) in blood pressure and LDL cholesterol (3-7 mg/dL). The high carbohydrate diet fared similar to the regular DASH diet. The diets high in protein and unsaturated fat had an additional slight reduction of blood pressure (1-2 mm Hg) and LDL cholesterol (about 2 mg/dL). The high protein diet had a slight decrease in HDL cholesterol (about 2 mg/dL) and was associated with reduced physical activity, reduced appetite, and bloating.
What to eat to be healthy remains mired in controversy. Nathan Pritikin and Dean Ornish demonstrated the benefits of reducing fat intake to 10% of the diet, but very few people are willing to stay on such a dietary program for the long haul. Moreover, Pritikin and Ornish failed to appreciate the health benefits of the monounsaturated and polyunsaturated oils. Atkins started a counterrevolution with the low-carbohydrate, high-protein pathway to weight loss. This works for some by reducing appetite and overall calories. Simple sugars drive hunger and protein seems to reduce it in some people.
However, the long-term health benefits of a high-protein diet, especially from animal sources, are highly questionable. Next comes the Mediterranean diet with its healthy oils and even moderate alcohol intake to reduce cardiovascular risk. The Europeans seems to be able to ingest this in moderation but Americans love large portions and have an epidemic of overweight and obesity. What are we to do?
This study adds some interesting knowledge to the dietary equation. The DASH diet, with its lower sodium, higher potassium and calcium, does reduce blood pressure and has a modest benefit on serum lipids. Advocates of Pritikin and Ornish criticize this diet as still much too high in fat (27%) which will not only fail to reduce atherosclerosis but also will continue its progression. However, the DASH diet is easily followed and is an improvement over the way most American eat. This study refines the knowledge of the DASH diet by confirming the benefits of the unsaturated oils, at least with lowering blood pressure and LDL cholesterol, albeit very modestly. No actual cardiac outcomes were part of this brief study of a small group of subjects. Higher protein intake also improved blood pressure and LDL cholesterol, but with a price of lowering HDL cholesterol and reduced physical activity. We all know physical activity may be even more important than nutrition in reducing cardiovascular risk.
How should we interpret these findings and use them in daily practice? Our patients vary greatly in what they like to eat. One diet has limited clinical usefulness in practice because only a subgroup of patients will follow it. We benefit by having multiple dietary pathways to improving cardiovascular risk. By keeping a 2-week food diary on our patients, we gain an understanding of how they like to eat. The "grazers" eat all day and the "carnivores" eat like a lion—one big meal. Using the principles of the DASH diet (low sodium, more vegetables, and adequate calcium), we can adjust a person's diet with respect to complex carbohydrates, proteins and healthy fats according to culture and personal preference.
Being a Dean Ornish fan, I am much more aggressive in my recommendations for reducing overall fat intake. Reducing body weight through healthy eating and increased physical activity is the most important clinical intervention we can make today with our patients. This study shows that our tool kit for dietary recommendations has options.
1. Weinberger MH. More novel effects of diet on blood pressure and lipids. JAMA. 2005;294:2497-2498.