Background: Dietary patterns characterized by high intakes of fruits and vegetables, whole grains, low-fat dairy products, and low glycemic load have been associated with lower type 2 diabetes mellitus (T2DM) risk. In contrast, dietary patterns that include high intakes of refined grains, processed meats, and high amounts of added sugars have been associated with increased T2DM risk.
Objective: This randomized, 2-period crossover trial compared the effects of dairy and sugar-sweetened product (SSP) consumption on insulin sensitivity and pancreatic β-cell function in men and women at risk of the development of T2DM who habitually consume sugar-sweetened beverages.
Methods: In a randomized, controlled crossover trial, participants consumed dairy products (474 mL/d 2% milk and 170 g/d low-fat yogurt) and SSPs (710 mL/d nondiet soda and 108 g/d nondairy pudding), each for 6 wk, with a 2-wk washout between treatments. A liquid meal tolerance test (LMTT) was administered at baseline and the end of each period.
Results: Participants were 50% female with a mean age and body mass index of 53.8 y and 32.2 kg/m2, respectively. Changes from baseline were significantly different between dairy product and SSP conditions for median homeostasis model assessment 2–insulin sensitivity (HOMA2–%S) (1.3 vs. −21.3%, respectively, P = 0.009; baseline = 118%), mean LMTT disposition index (−0.03 vs. −0.36, respectively, P = 0.011; baseline = 2.59), mean HDL cholesterol (0.8 vs. −4.2%, respectively, P = 0.015; baseline = 44.3 mg/dL), and mean serum 25-hydroxyvitamin D [25(OH)D] (11.7 vs. −3.3, respectively, P = 0.022; baseline = 24.5 μg/L). Changes from baseline in LMTT Matsuda insulin sensitivity index (−0.10 vs. −0.49, respectively; baseline = 4.16) and mean HOMA2–β-cell function (−2.0 vs. 5.3%, respectively; baseline = 72.6%) did not differ significantly between treatments.
Conclusion: These results suggest that SSP consumption is associated with less favorable values for HOMA2–%S, LMTT disposition index, HDL cholesterol, and serum 25(OH)D in men and women at risk of T2DM vs. baseline values and values during dairy product consumption.
Alex’s Notes: Believe it or not, by the time type-2 diabetes (T2DM) is diagnosed, the insulin secretory response if generally 70-80% below what would be a normal response level. Although much focus is placed on weight loss and exercise for T2DM prevention and treatment, there is no doubt that dietary factors play a central role. For instance, high intakes of fish, whole grains, dairy products, and an overall low glycemic load have been associated with lower risk, whereas high intakes of refined grains, processed meats, and added sugars are associated with an increased risk.
Of these foods, dairy deserves special attention. In the Health Professionals Follow-Up Study cohort of over 41,000 men, those who consumed more than 2.9 servings of dairy per day had a 23% lower relative risk of developing type-2 diabetes than those who consumed less than 0.9 servings per day. After full adjustment for confounding variables, each serving-per-day increase in total dairy intake was associated with a 9% lower risk for T2DM, and this was strongest for low-fat dairy (12%) and weakest for high-fat dairy (1%). I do find this last part odd, as we have previously seen dairy fat to be associated with glucose tolerance and insulin sensitivity, and whole-fat dairy consumption inversely associated with obesity.
Regardless, we also know that dairy is beneficial for metabolic syndrome through a variety of mechanisms. So with the above in mind, the current study researchers, with funding from the Dairy Research Institute, sought to examine how replacing sugar-sweetened beverages (SSBs) and foods with dairy products would affect insulin sensitivity and pancreatic β-cell function. One serving of dairy is 237mL (1 cup) of milk, 170g (6 ounces) of yogurt, or 30g (1 ounce) of cheese.
In a randomized crossover trial design, 33 men and women underwent two 6-week interventions separated by a 2-week washout period where they consumed sugar-sweetened products (SSP; 24oz SSB and 4oz vanilla soy pudding per day) or dairy products (2 cups of 2% milk and 6oz low-fat yogurt with no added sugar per day). The nutritional information for the intervention foods is provided in the table below. All subjects habitually consumed at least 24 ounces of SSB daily and were at high-risk for developing T2DM, but were otherwise healthy; the average age and BMI was 53 years and 32kg/m2, respectively. None habitually consumed more than 4 servings of dairy daily.
|Dairy Products||Sugar-sweetened Products|
|Low-fat Strawberry Yogurt (6 ounce)||
Vanilla Soy Pudding
Carbonated Cola Beverage
|Vitamin D, IU||100||80||60||0|
At the beginning and end of the interventions, everyone completed a 3-day food log, and it was shown that there were no significant differences between conditions for total energy intake. However, carbohydrate, sugar, and fiber intakes were significantly lower, and protein, total fat, and calcium significantly higher in the dairy condition relative to the SSP condition. I don’t have an explanation for the higher fiber intake in the SSP condition, although it was a difference of only 0.6 grams, making it essentially pointless, but the other nutrient differences were to be expected when considering the foods that each condition consumed.
Glucose homeostasis and blood lipids
There were no significant changes from baseline in the dairy condition for anything. However, in the SSP condition, fasting insulin increased, while insulin sensitivity and glucose deposition decreased. Additionally, the SSP condition significantly reduced HDL-c by 2mg/dL. Aside from these changes, there was nothing different between conditions. No differences in fasting glucose, 2-hour glucose or insulin, total AUC glucose or insulin, the Matsuda insulin sensitivity index (MISI), total cholesterol, LDL-c, or triglycerides.
But the authors did us proud
Despite the funding this study received, the authors conclude that this study does…
“…not clearly support beneficial effects of the dairy products consumed, because no marked changes in indicators of carbohydrate homeostasis from the habitual diet at baseline were observed during the dairy product condition.”
Nonetheless, the study does show some favorable outcomes for dairy consumption, and importantly, no detrimental outcomes, suggesting that dairy is not the end-all T2DM helper, but it definitely beats SSBs.