See the rest of the posts in this series here.
I’d hoped to be able to add a post to this series once or twice a week, and am finding it tricky to find the time. Darn day job. Anyway, if you want to see the collection of studies I’m pulling from for this series, it’s all pinned on my Inactivity and Metabolic Health pinterest board. I add new stuff there all the time.
The study I’m looking at today was part of the Heritage Family Study, which is a pretty massive undertaking looking at the role of genetics in a person’s cardiovascular and metabolic response to exercise. The Heritage Family Study is funded by grants from the NHLBI, which is one branch of the NIH. IE, the government. So naturally, some will dismiss this study as biased (anything government funded is highly suspect to a certain dogmatic faction of the alternative health and diet industry), although I’m not sure what investment the government has in getting people to exercise, other than improving public health and reducing health care costs. In any case, that’s a brief overview of the ‘parent’ study, take it as you will.
The Effects of Exercise Training on Glucose Homeostasis
This specific study was designed to
“…examine the effects of a 20-week endurance training program on insulin sensitivity, insulin secretion, and other IVGTT-derived [IVGTT=intravenous glucose tolerance test] variables while considering the potentially confounding effects of sex, race, age, and BMI.”
In other words, they wanted to see how people of different ages, genders, races and weight status responded to 20 weeks of exercise training. All participants were sedentary at study outset. 316 women and 280 men participated, so it’s a good sized study. The exercise protocol consisted of 3 session a week of cycling, starting at a duration of 30 minutes and increasing in intensity and duration to 50 minutes 3 times a week at study end. Each participant had an IVGTT before commencing exercise, and again very near the end of the 20 weeks (there was some variation in exact time of the second IVGTT due to availability and menstrual status of female participants, they wanted to ensure all the women were at the same stage of their cycle when the test was performed). Fasting plasma glucose and insulin were also tested 1 and 3 days after the last exercise session.One drawback of the study is that there was no control group, a limitation of the structure of the Heritage Family Study.
As you can probably expect, there were improvements across the board in metabolic parameters. Improved insulin sensitivity, glucose tolerance, insulin response, etc. There were also patterns in the differences in response between groups. Men and people with initially poorer metabolic responses saw greater improvements than women and those who were initially more metabolically healthy. There were some interesting findings in regard to a protective effect of exercise in regards to both hyperglycemia and the hunger and food seeking behaviors associated with hypoglycemia, as well as this tidbit:
“…the quartile with the [initially] lowest glucose tolerance registered an increase in insulin secretion following regular exercise. This increase in insulin secretion as well as the overall 11% increase in glucose effectiveness, which reflects the capacity of glucose to mediate its own disposal, may have contributed to the improvement in glucose tolerance.”
Ie, an increase in insulin secretion accompanied an increase in glucose effectiveness and tolerance. Insulin is not the bad guy. Insulin RESISTANCE is. And insulin resistance is caused by energy imbalance, inactivity and genetics. This study gives some insight into that genetic component.
There’s a lot of information here, and the full text of the study is available for free, so take a look, I try to keep these posts short and user friendly, so I won’t go into further detail here, and I’ll invite you to read the science for yourself.