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Abstract & Commentary
By Ralph R. Hall, MD, FACP, FACSM, Professor of Medicine Emeritus, University of Missouri at Kansas City. Dr. Hall reports no financial relationship to this field of study.
Synopsis: An increase in dairy food intake produces significant and substantial suppression of oxidative and inflammatory stress associated with overweight and obesity.
Source: Zemel MB, et al. Effects of dairy compared with soy on oxidative and inflammatory stress in overweight and obese subjects. Am J Clin Nutr 2010;91:16-22.
The objective of this study was to evaluate the acute effects of a dairy-rich diet on oxidative and inflammatory stress in overweight and obese subjects in the absence of changes in adiposity. Previous studies performed by the authors had demonstrated that dairy-rich products had markedly reduced inflammatory markers in obese mice.
Twenty subjects (10 obese and 10 overweight) participated in a blinded, randomized, crossover study of dairy compared with soy-supplemented eucaloric diets. Two 28-day dietary periods were separated by a 28-day washout period. Inflammatory and oxidative stress biomarkers were measured on days 0, 7, and 28 of each dietary period.
The dairy-supplemented diet resulted in significant suppression of oxidative stress (plasma malondialdehyde, 22%; 8-isoprotane-F alpha, 12%; P < 0.0005). Inflammatory markers decreased as shown in the Table.
Soy exerted no significant effect. There were no significant differences in response to treatment in overweight and obese subjects.
Other findings of note were a decrease in C-reactive protein (57%) in the dairy-treated subjects, and a significant decrease in LDL cholesterol (-8.9 mg/dL with the dairy supplement compared with +2.9 mg/dL with the soy supplement.)
The authors concluded that an increase in dairy food intake produced significant and substantial suppression of oxidative and inflammatory stress associated with overweight and obesity.
This is an interesting and timely report. There is a concern that some women are likely to replace their dairy products with soy, in view of the recent reports from China, that diets high in soy are associated with a decrease in breast cancer.1
The two diets (dairy and soy) in the form of smoothies were administered 3 times per day throughout each 28-day treatment period. Each smoothie contained 170 Kcal, 10 g protein, 1 g of fat, and 30 g carbohydrate. The dairy smoothies were milk-based, with non-fat milk as the protein source.
The authors note that it is well established that excess adiposity results in an increase in both reactive oxygen species and inflammatory cytokine production and a corresponding suppression of anti-inflammatory cytokine production. This phenomenon is regulated, in part, by calcitriol. The authors have previously reported that a reduction in calcitriol reduces oxidative and inflammatory stress in mice fed with high-calcium diets compared with low-calcium diets. They also demonstrated that non-fat dry milk elicited a significantly greater response than calcium carbonate.2
Findings in studies using low-fat dairy products continue to stimulate research about their nutritional effects. Low-fat dairy products are an important constituent in the Dietary Approach to Stop Hypertension (DASH ) diet.3 A recent study from the University of Minnesota examining beverage habits and other dietary parameters in a 5-year prospective analysis of 2294 adolescents showed no association between sugar-sweetened beverage consumption and adolescent weight gain. However, adolescents who consumed little or no white milk gained significantly more weight than their peers who consumed white milk.4
The authors point out that it is not possible to determine which effects were mediated by calcium or other components of the milk. For instance, milk contains angiotensin-converting enzyme-inhibiting peptides, whereas adipose tissue expresses all components of the renin angiotensin system. Pharmacologic antagonism of this system suppresses oxidative stress.5
In addition the authors have previously shown that leucine in milk may contribute to the reduction in oxidative and inflammatory stress.6 Leucine stimulates muscle protein synthesis and inhibits protein degradation and suppresses energy storage in adipose tissue.
This work was supported by The National Dairy Council. However, the authors previous effort in this field and the rigorous documentation and presentation of their data, support the importance of this study.
1. Shu XO, et al. Soy food intake and breast cancer survival. JAMA 2009;302:2437-2443.
2. Zemel MB, Sun X. Dietary calcium and dairy products modulate oxidative and inflammatory stress in mice and humans. J Nutr 2008;138:1047-1052.
3. Sacks FM. Rational and design of the Dietary Approach to Stop Hypertension trial (DASH). A multicenter controlled-feeding study of dietary patterns to lower blood pressure. Ann Epidemiol 1995;5:108-118.
4. Vanselow MS, et al. Adolescent beverage habits and changes in weight over time: Findings from Project EAT. Am J Clin Nutr 2009;90:1489-1495.
5. Shah NP. Effects of milk-derived peptides: An overview. Br J Nutr 2000;84(Suppl 1):S3-S10.
6. Sun X, Zemel MB. Leucine modulation of mitochondrial mass and oxygen consumption in skeletal muscle cell and adipocytes. Nutr Metab 2009;6:26.