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Effects of Dairy on Metabolic Syndrome Parameters: A Review


Metabolic syndrome (MetS), characterized by central obesity, dyslipidemias, hypertension, and hyperglycemia, impacts 34 percent of the U.S. adult population. MetS has been demonstrated to be affected by dietary components. Data from epidemiological studies and clinical interventions suggest that one or more dairy components might directly affect MetS parameters. For example, calcium has been postulated to reduce body weight by modulating vitamin D concentrations in plasma and therefore attenuating intracellular calcium effects in activating genes involved in fatty acid synthesis and reducing those involved in lipolysis. Peptides present in milk have been associated with the inhibition of angiotensin converting enzyme and, therefore, with blood pressure reductions. Branched chain amino acids may increase post-prandial insulin secretion and regulate plasma glucose levels, and leucine, an abundant amino acid in milk, may be responsible for decreased plasma glucose through modulation of mTOR. Through different proposed mechanisms, dairy nutrients may target all components of MetS.

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Alex’s Notes: Metabolic syndrome is a precursor condition. Although it also has negative health effects, metabolic syndrome is mainly tool to identify persons at risk for developing more serious and crippling chronic diseases. As the authors of this review state, “it has therefore become a necessity to control MetS by lifestyle changes before it progresses to T2D or CVD.” I’m a huge fan of the promotion of lifestyle changes to treat the cause rather than other methods that merely treat the symptoms, and an important part of our lifestyle is our dietary habits. Many dietary changes from low-carbohydrate to Mediterranean to ancestral have all been recommended to manage MetS, but even the inclusion of specific foods or food components such as eggs and fiber have been shown to be beneficial. And now, one more food product enters the realm as a potential therapeutic approach to MetS: dairy.

Milk is about 89% water, 3.5% protein, 4.6% carbohydrate, and 3.3% fat. Of course these values can all vary depending on the type of milk, and even more so when looking at milk-based products like yogurt and cheese. What won’t change is the high-quality protein. Bovine milk protein is 80% casein and 20% whey by nature, both of which are some of the highest biologically rated proteins that we know of. The fat is mostly saturated, but a solid 10% is short- and medium-chained fatty acids that are directly oxidized by the liver rather than being incorporated into fat for storage.

Now, I’m definitely no fan of epidemiology, but it does hold a strong track record to the benefits of dairy. For example, The CARDIA study did a ten year follow-up on just over 3,000 adults from four major metropolitan areas in the US and found a 72% risk reduction for developing MetS in persons consuming more than five servings of dairy daily compared to those consuming 1.5 servings of dairy daily. Moreover, a systemic review of observational evidence found that comsuming three to four servings of dairy per day decreased the risk of developing MetS by 29% compared to consuming less than two servings per day. In fact, most of the observational evidence supports the protective notion of dairy. However, they do differ in the amount of protection, and they are only associations – not causal.

This is where controlled clinical trials come in useful. In weight stable overweight or obese subjects, increasing dairy consumption to three or more servings daily has been reported to reduce various parameters of metabolic syndrome, including oxidative and inflammatory stress. Of course, not all studies have shown support for dairy. One such trial found no benefit to consuming four servings daily compared with one or less. However, the trial was short-lived at 12 weeks and had the subjects on a calorically restricted diet, which may overshadow the benefits of dairy simply because losing weight is guaranteed to improve all parameters of MetS. Conversely, the beneficial studies above had the weight-stable participants merely add the dairy into their normal diets.

Regardless, based on the benefits of dairy consumption reported in observational studies and randomized control trials, it’s been estimated that the total disease burden cost could be reduced by $26 billion in the US if adults consumed 3-4 servings of dairy per day. And that is just in the first year. The estimated five years savings are in excess of $200 billion.

Several theories about dairy have arisen to explain its beneficial effects. Dairy is the poster-child for calcium, and it has been proposed that lowered adipose calcium concentrations, resulting from increased dietary calcium, decreases lipogenesis and directly stimulates lipolysis. This is because when serum calcium levels fall, a chain of events occur that increase 25(OH)D (active form of vitamin D), which acts to increase the concentration of calcium inside fat cells. When fat cell calcium concentrations increase, genes that regulate fat synthesis are activated, and thus when you consume dietary calcium this entire chain-of-events is averted. It is interesting that this explanation is incongruent with observations of reduced vitamin D levels in the obese, but then again, since when has epidemiology been right? Moreover, a review of 15 cross-sectional studies found an inverse association between dairy intake and BMI in the majority of the studies, and fancy statistical stuff of 18 prospective studies found a 1.1 BMI decrease by increasing dietary calcium from 400 to 800 mg/day.

Calcium from dairy may also help control blood pressure by decreasing serum 25(OH)D levels and preventing the calcium-mediated vasoconstriction of smooth muscle, but the main effects are through dairy protein. And yes, I am referring to the fitness community’s wannabe Gods – whey and casein. The primary mechanism for blood pressure regulation in the body involves the Renin-Angiotensin II-Aldosterone pathway, and somewhere along the way you get the production of angiotensin II, which acts to increase blood pressure. By inhibiting it, you decrease blood pressure. Both whey and casein include ACE (the enzyme that activated angiotensin II) inhibiting peptides that are released during digestion. A lot of data supports whey in the reduction of blood pressure, but casein is more variable because it coagulates in the stomach, making it more difficult to digest and thus slows delivery of the antihypertensive peptides.

Then you have the blood glucose control benefits of diets that are higher in protein. The idea is that a protein-induced increase in insulin increases hepatic regulatory controls of glucose production and increases glucose disposal through the mTOR pathway. We know that whey is highly insulinogenic, and it has been proposed that when carbohydrates are replaced with protein, the branched chained amino acids (BCAAs) – specifically leucine – will “shift” the regulatory control of glucose homeostasis away from the pancreas and insulin secretion toward hepatic control through gluconeogenesis.

Overall, this review from the Department of Nutritional Sciences at the University of Connecticut provides a lot of interesting theories and hypotheses for why dairy is beneficial to MetS. While it is unlikely that simply consuming more dairy will fix everything, the evidence supports the notion that it will help. Combine it with adequate sleep and strenuous exercise, and you have a recipe for success. Also, as the authors point out,

“Including ~3 servings of dairy into the diet per day requires only slight dietary modifications, making it an easy lifestyle change to maintain.”

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