Diabetes is a major risk factor for coronary heart disease and is the sixth leading cause of death in the United States. The most prevalent form of diabetes, type 2 diabetes, usually appears in adults, often in middle age, and is responsible for nearly 200,000 U.S. deaths per year. Type 2 diabetes is a progressive disease in which the pancreas produces insulin, but the body is unable to use the insulin effectively. The body's cells become resistant to the action of insulin, usually due to defective or reduced numbers of insulin receptors. Individuals at the highest risk for developing type 2 diabetes are often overweight or obese, have family members with the disease, and have Metabolic Syndrome (MetS), also termed Insulin Resistance Syndrome. MetS is an increasingly common disorder in the U.S. characterized by abdominal obesity, high blood pressure, elevated blood glucose, high triglycerides and low HDL ("good") cholesterol (HDL-C). Diagnosis is based on the presence of at least three of the five characteristics. Sixty million people in the United States have MetS, and 1 in 4 will go on to develop type 2 diabetes.
Key recommendations for preventing and managing MetS include: weight loss, increased physical activity and dietary changes. Recommended dietary changes follow the 2005 Dietary Guidelines and include reducing calories while developing healthy eating habits that incorporate a diet low in saturated fat, trans fat and cholesterol, and increased consumption of low fat dairy products, fruits, vegetables, and whole grains. The role of diet and the influences of specific categories of foods and/or nutrients are emerging as important factors in the prevention and management of MetS.
Dairy, Metabolic Syndrome and Type 2 DiabetesA growing body of observational and clinical evidence has emerged showing that adequate dairy product consumption is inversely associated with abdominal obesity, high blood pressure and high blood glucose suggesting that dairy foods may play a significant role in reducing the risk of Met-S and type 2 diabetes. For example, in an observational study of nearly 5,000 men and women, greater than 1 serving per day of milk products was associated with a 40% lower risk of MetS in men. Perhaps the largest study to examine the relationship of milk and MetS is the CARDIA study (Coronary Artery Risk Development in Young Adults), which examined the association between dairy foods intake and incidence of MetS in 3,157 men and women ages 18 to 30 over a 10-year period. Results showed a reduction in all MetS characteristics with increased dairy consumption, including significant reductions in the incidence of obesity, hypertension, abnormal blood glucose levels and dyslipidemia (low serum HDL cholesterol and high serum triglyceride concentrations) in individuals who were overweight and obese, but not normal-weight at baseline. The odds of developing MetS was 72% lower in individuals consuming five or more dairy servings per day compared to 1.5 servings, with each eating occasion of dairy foods contributing to a 21% reduction in the odds for MetS. Three or more daily servings were found to have the most benefit suggesting that the recommendations by the 2005 Dietary Guidelines for Americans to consume at least three servings of dairy foods a day may help protect overweight individuals from developing MetS, and may help reduce the risk of type 2 diabetes and coronary heart disease. Other observational studies have also found that dietary patterns with higher dairy intake may help lower the risk of these conditions. In middle aged and older women, for example, higher intakes of calcium and dairy products were significantly and inversely associated with the prevalence of MetS. In another study, subjects consuming at least three dairy servings per day had lower odds of developing MetS compared to those consuming less than 1.7 servings per day. Finally, in a study of middle aged or older women followed for 10 years, it was shown that each additional daily serving of dairy was associated with a 4% lower risk of type 2 diabetes, while in another study of men, a 9% lower risk was observed over a 12-year period.
Dairy Helps Lower Symptoms of Metabolic SyndromeHigh Blood Pressure
High blood pressure affects nearly 65 million people in the United States and is a key component of MetS, and is a risk factor for type 2 diabetes and coronary heart disease. Numerous studies over the years have revealed that diet and the nutrient components in certain foods, including dairy products, can play a significant role in the management of high blood pressure. In the well known DASH study (Dietary Approaches to Stop Hypertension), which evaluated the effects of a healthy diet on blood pressure, 459 subjects with elevated and high blood pressure were placed on one of three diets for eight weeks: a control "typical American diet;" a diet containing high amounts of fruits and vegetables and fiber (F+V) (8-10 servings per day); or a diet high in fruits and vegetables plus three servings of dairy products and lower in fat/saturated fat (DASH diet). Results showed that the combination of fruits, vegetables and low-fat dairy, "DASH diet," resulted in the greatest reductions in both systolic blood pressure and diastolic blood pressure compared to the "typical American diet," whereas the F+V diet that excluded dairy products was about half as effective as the DASH diet. In a subsequent study, the DASH diet was further tested against diets containing typical or reduced levels of sodium. Results showed that while reducing sodium significantly lowered blood pressure, the DASH diet resulted in even greater clinically significant reductions in blood pressure at all levels of sodium tested. These studies along with others have clearly demonstrated the value of a healthy diet containing three servings a day of low-fat dairy products and high in fruits and vegetables for the management of high blood pressure that may also be effective in reducing the risk of MetS.
Obesity and Body FatAbout 127 million adults in the United States are overweight, 60 million are obese, and 9 million are severely obese. This growing problem in the United States is leading to more individuals with increased risk of MetS, type 2 diabetes and coronary heart disease. This is an especially acute problem in those with high abdominal fat, one of the primary characteristics of MetS.
Observational and clinical evidence indicate that dairy foods may be effective in reducing body weight and fat in obese individuals. The CARDIA study found that the incidence of obesity and weight gain risk was 67% lower in those consuming the most dairy products versus those consuming the least. Moreover, a recent clinical study has evaluated the effects of increasing dairy and calcium intake on body weight and fat loss in obese subjects consuming calorie reduced weight loss diets for six months. Three diets with the same levels of protein, fat, and carbohydrate were tested: a low calcium control diet (<500 mg/day) with little or no dairy products; a diet with adequate calcium provided predominantly by calcium supplements (total: 1,200 - 1,300 mg Ca/day); and a diet adequate in calcium provided predominately by three servings of dairy products as milk, yogurt, and cheese (total: 1,200 - 1,300 mg Ca/day). The greatest weight loss occurred in subjects on the dairy diet, losing 24.4 lbs. versus an 18.9 lbs. loss in the calcium supplement group, and a 14.5 lbs. loss in the low calcium/low dairy diet group. Those on the dairy diet also lost a greater amount of body fat and trunk fat compared to the other two groups. Excess trunk fat, which includes abdominal fat, is a risk factor for MetS and type 2 diabetes. These results are consistent with other studies using dairy foods in a calorie reduced weight loss diet and showed similar reductions in body weight and body fat. Thus, a growing body of evidence suggests that consuming three servings a day of dairy products, in a calorie reduced weight loss diet, can accelerate loss of body weight and body fat in obese and overweight individuals compared to consuming little or no dairy and may help in the prevention and management of MetS.