Obesity and type 2 diabetes

A large share of the on-going increase in prevalence of type 2 diabetes is driven by the obesity epidemic (1, 2), and it is therefore relevant to assess the role of milk and dairy products for body weight control. Childhood overweight and obesity worldwide is a major contributor to the current obesity epidemic, and childhood obesity frequently tracks into adulthood (3). Therefore, early prevention of childhood obesity is important. A meta-analysis showed that among children in the pre-school and school age, there was no association between dairy intake and adiposity (4). However, there was a modestly protective effect in adolescence. A recent meta-analysis by Lu et al. (5) found that children in the highest dairy intake group were 38% less likely to be overweight or obese compared to those in the lowest dairy intake group. An increase in dairy intake of one serving per day was associated with a 0.65% lower body fat and a 13% lower risk of overweight or obesity.

Milk and dairy products are good sources of high-quality protein. Protein is important during weight loss and subsequent weight maintenance due to the high satiating effect which helps to prevent over-consumption of energy and thereby reduces body fat stores (6, 7). Furthermore, dairy protein is a good source of essential amino acids for muscle protein synthesis and thus helps to maintain the metabolically active muscle mass during weight loss (8). Meta-analyses support that in adults, dairy products facilitate weight loss and improve body composition, that is, reduce body fat mass and preserve lean body mass during energy restriction and in short-term studies (9–11). The effect of an increased dairy consumption on body weight in long-term studies (>1 year) and in energy balance studies is less convincing (10, 11). This is likely due to the opposing effects of dairy on body composition, that is, reduction of fat mass and preservation of lean body mass.

Meta-analyses assessing the role of intake of milk and dairy products on risk of type 2 diabetes have consistently found no or a slight beneficial effect of dairy intake on diabetes risk (12–15). This is consistent with a Mendelian randomisation study using genetic polymorphisms for the lactase gene, which showed that milk intake assessed by lactose tolerance was not associated with risk of type 2 diabetes or obesity (16). The most recent meta-analysis on dairy intake and diabetes incidence included 22 cohort studies with a total of 579,832 subjects and 43,118 type 2 diabetes cases (17). An inverse association between total dairy and yoghurt intake and risk of type 2 diabetes was reported although there was no association with milk intake. The benefits of fermented dairy products (cheese and yoghurt) in relation to type 2 diabetes may be due to their effect on the gut microbiota (18, 19). Other studies have identified that whey protein (primarily in milk and yoghurt) can reduce postprandial plasma glucose concentration in type 2 diabetic subjects (20). This effect may be due to the branched chain amino acids in the whey protein fraction, particularly leucine which has been shown to induce a greater stimulation of glucose-dependent insulinotropic polypeptide (GIP), but not glucagon like peptide 1 (GLP-1), compared to other amino acids (21). The GIP response is possibly a key factor in the higher insulin response and the subsequent lowering of blood glucose seen after whey ingestion, at least in healthy subjects. In addition to the insulinotropic effect of milk, a recent study has indicated that dairy may also improve insulin sensitivity (22).

Conclusion on obesity and type 2 diabetes

A diet high in milk and dairy products reduces the risk of childhood obesity and improves body composition in adults. This likely contributes to lower the risk of developing type 2 diabetes. Additionally, dairy product consumption during energy restriction facilitates weight loss, whereas the effect of dairy intake during energy balance is less clear. Finally, there is increasing evidence suggesting that especially the fermented dairy products, cheese and yoghurt, are associated with a reduced risk of type 2 diabetes.

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