Dairy and weight loss hypothesis: an evaluation of the clinical trials

Dairy products and metabolic effects in overweight men and women: results from a 6-mo intervention study

BACKGROUND

Some epidemiologic studies have suggested inverse relations between intake of dairy products and components of the metabolic syndrome.

OBJECTIVE

The objective was to investigate the effects of an increased intake of dairy products in persons with a habitually low intake on body composition and factors related to the metabolic syndrome.

DESIGN

Middle-aged overweight subjects (n = 121) with traits of the metabolic syndrome were recruited in Finland, Norway, and Sweden and randomly assigned into milk or control groups. The milk group was instructed to consume 3-5 portions of dairy products daily. The control group maintained their habitual diet. Clinical investigations were conducted on admission and after 6 mo.

RESULTS

There were no significant differences between changes in body weight or body composition, blood pressure, markers of inflammation, endothelial function, adiponectin, or oxidative stress in the milk and the control groups. There was a modest unfavorable increase in serum cholesterol concentrations in the milk group (P = 0.043). Among participants with a low calcium intake at baseline (<700 mg/d), there was a significant treatment effect for waist circumference (P = 0.003) and sagittal abdominal diameter (P = 0.034). When the sexes were analyzed separately, leptin increased (P = 0.045) and vascular cell adhesion molecule-1 decreased (P = 0.001) in women in the milk group.

CONCLUSIONS

This study gives no clear support to the hypothesis that a moderately increased intake of dairy products beneficially affects aspects of the metabolic syndrome. The apparently positive effects on waist circumference and sagittal abdominal diameter in subjects with a low calcium intake suggest a possible threshold in relation to effects on body composition.

Effects of a fibre-enriched milk drink on insulin and glucose levels in healthy subjects

Background

The glycaemic response to foods is dependent on the quality and content of carbohydrates. Carbohydrates in the form of dietary fibre have favourable effects on insulin and glucose metabolism and may help to control energy intake. Dairy products have a relatively low carbohydrate content, and most of the carbohydrate is in the form of lactose which causes gastrointestinal symptoms in part of the population. In order to avoid these symptoms, dairy products can be replaced with lactose-free dairy products which are on the market in many parts of the world. However, the effects of lactose-free products on insulin and glucose metabolism have not been studied.

Methods

In the present study, we investigated the effects of 1) a lactose-free milk drink, 2) a novel fibre-enriched, fat- and lactose-free milk drink and 3) normal fat-free milk on serum glucose and insulin levels and satiety using a randomized block design. Following an overnight fast, 26 healthy volunteers ingested 200 ml of one of these drinks on three non-consecutive days. Insulin and glucose levels and subjective satiety ratings were measured before the ingestion of the milk product and 20, 40, 60, 120 and 180 minutes after ingestion. The responses were calculated as the area under the curve subtracted by the baseline value (AUC minus baseline).

Results

The insulin response was significantly lower for the fibre-enriched milk drink than it was for the other milk products (AUC, P = 0.007). There were no differences in the response for glucose or in the AUC for the subjective satiety ratings between the studied milk products.

Conclusion

The present results suggest that this novel milk drink could have positive effects on insulin response.

Milk intake and the risk of type 2 diabetes mellitus, hypertension and prostate cancer

Milk intake is widely recommended for a healthy diet. Recent evidences suggest that milk/dairy products are associated with a lower risk of type 2 diabetes and hypertension. On the other hand, high calcium intake has been associated with a higher risk of prostate cancer. The calcium and vitamin D content in dairy foods could have beneficial effects on glucose metabolism and renin/angiotensin system as well regulates body weight. The association between high dairy/calcium consumption and prostate cancer risk are related to the presence of estrogens and insulin like growth factor (IGF-I) in milk. Based on the current evidence, it is possible that milk/dairy products, when consumed in adequate amounts and mainly with reduced fat content, has a beneficial effect on the prevention of hypertension and diabetes. Its potential role in the pathogenesis of prostate cancer is not well supported and requires additional study.

Should dairy be recommended as part of a healthy vegetarian diet? Counterpoint

Although cow milk has been widely recommended in Western countries as necessary for growth and bone health, evidence collected during the past 20 y shows the need to rethink strategies for building and maintaining strong bones. Osteoporotic bone fracture rates are highest in countries that consume the most dairy, calcium, and animal protein. Most studies of fracture risk provide little or no evidence that milk or other dairy products benefit bone. Accumulating evidence shows that consuming milk or dairy products may contribute to the risk of prostate and ovarian cancers, autoimmune diseases, and some childhood ailments. Because milk is not necessary for humans after weaning and the nutrients it contains are readily available in foods without animal protein, saturated fat, and cholesterol, vegetarians may have healthier outcomes for chronic disease if they limit or avoid milk and other dairy products. Bones are better served by attending to calcium balance and focusing efforts on increasing fruit and vegetable intakes, limiting animal protein, exercising regularly, getting adequate sunshine or supplemental vitamin D, and getting approximately 500 mg Ca/d from plant sources. Therefore, dairy products should not be recommended in a healthy vegetarian diet.

Dairy product consumption and the metabolic syndrome

The metabolic syndrome is an important risk factor for type 2 diabetes mellitus and CVD. Epidemiological studies have now suggested protective effects of dairy product consumption on the development of this syndrome. Here we review the physiological effects and possible mechanisms involved of three main dairy constituents (Ca, protein, fat) on important components of the metabolic syndrome. Ca supplements improve the serum lipoprotein profile, particularly by decreasing serum total and LDL-cholesterol concentrations. They also lower systolic and diastolic blood pressure. Insufficient evidence exists for a significant role of Ca supplements or dairy in body-weight management. Effects of Ca may be related to intestinal binding to fatty acids or bile acids, or to changes in intracellular Ca metabolism by suppressing calciotropic hormones. Dietary proteins may increase satiety in both the short and longer term, which may result in a reduced energy intake. They have also been reported to improve the serum lipoprotein profile as compared with carbohydrates. Dairy proteins are precursors of angiotensin-I-converting enzyme-inhibitory peptides, which may lower blood pressure. Such effects, however, have inconsistently been reported in human studies. Finally, conjugated linoleic acid, which effectively lowers body weight in animals, has no such effect in humans in the quantities provided by dairy products. To reduce the intake of SFA, the consumption of low-fat instead of high-fat dairy products is recommended. In conclusion, more research is warranted to better understand the physiological effects and the mechanisms involved of dairy products in the prevention and treatment of the metabolic syndrome.

Review of the effect of dairy products on non-lipid risk factors for cardiovascular disease

The association between dairy food consumption and the risk of cardiovascular disease (CVD) has been a topic of intense debate over the years. Recent data suggest that individuals who consume dairy foods, particularly low fat products, are less likely to develop CVD than those who have a lower intake of these foods. We are also just beginning to understand how various components of the complex dairy food matrix affect several risk factors for CVD. The objective of this review is to provide an overview of the effects of dairy foods per se and of some of their components on non lipid CVD risk factors. Focus will be on blood pressure, inflammation, insulin resistance and type 2 diabetes, obesity and the metabolic syndrome. While the impact of dairy foods on blood pressure appears to be beyond debate, their effects on body weight and other non lipid risk factors need to be further substantiated. However, the purported inverse association between dairy foods, particularly low fat dairy products, and the metabolic syndrome is suggestive of cardiovascular benefits that may go well beyond the effect of dairy fat on blood cholesterol.