Impact of a high Intake of Dairy Product on Insulin Sensitivity in Hyperinsulinemic Adults: A Cross-Over Randomized Controlled Trial
Sarah O’Connor, Pierre Julien, Stanley John Weisnagel, Claudia Gagnon, Iwona Rudkowska
Current Developments in Nutrition, Published: 24 July 2019
https://doi.org/10.1093/cdn/nzz083
Abstract
Background
Dairy product intake has been associated with decreased risk of type 2 diabetes (T2D) in cohort studies. However, results from clinical trials on T2D-related risk factors remain inconclusive.
Objective
The objective of this clinical trial is to evaluate the impact of increased dairy product intake (HD) (≥ 4 servings/day) for 6 weeks, compared with an adequate dairy product intake (AD) (≤ 2 servings/day), on glycemic and insulinemic parameters, insulin sensitivity, insulin secretion and beta-cell function in hyperinsulinemic adults.
Methods
In this cross-over clinical trial, hyperinsulinemic adults were randomized to HD or AD for 6 weeks, than crossed-over after a 6-week washout period. Serum glucose, insulin, C-peptide, HOMA-IR, Matsuda index, insulinogenic index and disposition index were measured and analyzed using a repeated measures mixed model adjusted for age, sex and BMI. Anthropometric measures were collected and food intake was evaluated using a validated food frequency questionnaire.
Results
Nineteen males and 8 females completed the study (mean ± SD: age:55 ± 14 y, BMI:31.3 ± 3.3 kg/m2. Dairy product intake was 5.8 servings/day in HD and 2.3 servings/day in AD after 6 weeks. No difference was observed between HD and AD after 6 weeks for all outcomes.
Conclusions
High dairy product does not affect glycemic and insulinemic parameters, insulin sensitivity, insulin secretion and beta-cell function over an adequate intake in hyperinsulinemic adults. Additional larger and longer studies assessing T2D-related risk factors are required. Registration number: Clinicaltrials.gov (NCT02961179).1
Comment
I had, in my earlier years in practice, expressed some concern about the insulinergic (insulin increasing) effect of dairy. As early as 1997 Holt and colleagues had demonstrated that foods could have insulin responses that were vastly different from their glycaemic index.2 In other words, some foods seemed to have much greater insulin responses than blood-sugar responses and this could potentially be problematic for those with metabolic disorder and insulin resistance and might pose a problem for people wanting to lose fat or remain metabolically healthy. However, even this early research did show that, with some exceptions, there were general trends, including that glycaemic load (total carb content per 100 g) and sugar did have a strong association with insulin response, while protein content and fibre generally had a negative association with insulin (i.e. the more protein and the more fibre in a food, the lower the insulin response overall). However, protein does elicit an insulin response, and this can be as large as that of carbohydrate, so, there is always going to be insulin released in response to protein-containing foods. We need to remember that this is not a bad thing! Insulin is not the universal bogey man than many in low-carb circles have painted it as. Insulin aids the clearance of substrate (glucose, but also amino acids and beneficial compounds like creatine) from the blood into tissue for use, and inhibits hepatic glucose output and gluconeogenesis.
Insulin is not a strong independent indicator of risk for obesity or other metabolic challenges. So, on balance, insulin is not a problem per se. It is only when metabolic disorder/insulin resistance and hyperinsulinaemia are present and growing that the interplay between insulin release and resistance is a problem in and of itself.
There will be significant variation in the insulin and glycaemic responses between foods, between individuals,3, 4 and even from time-to-time in an individual,5 and even factors like the polyphenol antioxidant content of a meal could improve glucose response.6 An incredibly interesting study from Zeevi et al. found that there was large variability in the glucose responses to different foods between people (and that this was linked to metabolic health and to individuality of the microbiome) and when people were allocated to eat foods that they had the lowest blood glucose responses to, not surprisingly, their post-meal glucose responses were better and there were positive changes to the microbiome.7
However, on balance, in mixed meals, in a mixed diet that is based on natural, unrefined foods, variation in glucose and insulin responses to foods is to be expected and should not cause concern, and nor should the insulin response to dairy itself.
The evidence has become quite clear that milk and dairy overall are not associated with diabetes or metabolic syndrome and assuming you can tolerate dairy, could actually be protective against it, along with other benefits to health. This study helps to confirm that there is no significant or meaningful effect of an increase in dairy intake on insulin and blood glucose homeostasis.
The evidence has become quite clear that milk and dairy overall are not associated with diabetes or metabolic syndrome
References
1. O’Connor S, Julien P, Weisnagel SJ, Gagnon C, Rudkowska I. Impact of a high Intake of Dairy Product on Insulin Sensitivity in Hyperinsulinemic Adults: A Cross-Over Randomized Controlled Trial. Current Developments in Nutrition. 2019.
2. Holt S, Miller J, Petocz P. An insulin index of foods: the insulin demand generated by 1000-kJ portions of common foods. The American journal of clinical nutrition. 1997;66(5):1264-76.
3. Jenkins DJ, Wolever TM, Wong GS, Kenshole A, Josse RG, Thompson LU, et al. Glycemic responses to foods: possible differences between insulin-dependent and noninsulin-dependent diabetics. The American Journal of Clinical Nutrition. 1984;40(5):971-81.
4. Venn BJ, Green TJ. Glycemic index and glycemic load: measurement issues and their effect on diet–disease relationships. European Journal Of Clinical Nutrition. 2007;61:S122.
5. Vega-López S, Ausman LM, Griffith JL, Lichtenstein AH. Interindividual Variability and Intra-Individual Reproducibility of Glycemic Index Values for Commercial White Bread. Diabetes Care. 2007;30(6):1412-7.
6. Thompson LU, Yoon JH, Jenkins DJA, Wolever TMS, Jenkins AL. Relationship between polyphenol intake and blood glucose response of normal and diabetic individuals. The American Journal of Clinical Nutrition. 1984;39(5):745-51.
7. Zeevi D, Korem T, Zmora N, Israeli D, Rothschild D, Weinberger A, et al. Personalized Nutrition by Prediction of Glycemic Responses. Cell. 2015;163(5):1079-94.
