In Type 2 Diabetics the insulin produced by beta-cells of the pancreas is no longer able to drive uptake of glucose into cells (insulin resistance). Beta-cells attempt to compensate for this deficiency by increasing their production of insulin. However, this upregulation is short-lived and the beta-cells will eventually fail entirely. In this situation, if an individual’s insulin resistance is eventually managed or reversed, they will be presented with a new problem – their beta-cells can no longer produce insulin and the individual will need to manage their insulin with injections/pumps just like a Type 1 Diabetic. Exercise is known to improve insulin resistance in a variety of individuals. Following this observation Nieuwoudt and co-authors (2017) conducted a study to determine if a CrossFit (functional high intensity) training program would also increase beta-cell function in adults with Type 2 diabetes.
The Takehome: There are a lot of potential limitations whenever one conducts a study in humans, but this study handles them well. CrossFit Games athlete Julie Foucher, MD was an author of this study so the CrossFit training was applied appropriately. This study showed that high intensity CrossFit training for as little as 10-20 min/day, 3 days/wk for 6 weeks improved beta-cell function and insulin processing efficiency in adults with Type 2 diabetes. However, overall glucose tolerance (the ability of the body’s cells to take up glucose from the bloodstream) was not significantly improved as some of the participants were unable to produce much, if any, insulin from the start of the study (beta-cell failure). In those participants where their beta-cells could still produce insulin, glucose intolerance was improved after 6 weeks of training suggesting that, in order for high intensity CrossFit training to improve beta-cell function, it must be employed before the cells have reached failure.
- 12 adults with Type 2 Diabetes were studied (8 women, 4 men)
- Exercise was 6 weeks of CrossFit Training 3-4 times per week.
- Participants received a standardized mixed-meal dinner (55% carbohydrate, 30% fat, 15% protein) the night before testing.
- A variety of blood/serum markers were measured before and after the 6 weeks of training.
- Beta-cell function (DI) was individually calculated as the product of the secretory index and insulin sensitivity index x10^3 (an accepted clinical standard).
- Body fat percentage decreased after 6 weeks of training.
- Beta-cell function significantly improved after 6 weeks of training.
- The proinsulin/insulin ratio, a measure of insulin processing inefficiency, was reduced after 6 weeks of training.
- Changes in beta-cell function were significantly correlated with insulin secretion.
- Overall, glucose tolerance was not improved after 6 weeks of training.
- Glucose tolerance did improve in the subgroup of individuals who had better beta-cell secretory capacity at the beginning of the study.
- There is no control group.
- The sample size of the study is small.
- The small small size of the study was limited further by the fact that two sexes, unequally represented, comprise the study group. However, the authors make note of potential sex differences and the need for further investigation.