There has been some recent buzz about Intermittent Fasting and the effects it has on body composition and weight loss. There are limited human studies on Intermittent Fasting, and a select number of comparison studies have only been completed on mice. Human studies were few and limited to fasting during Ramadan. As a result, I tailored my search to mice and was able to find a randomized controlled study through PubMed with statistically significant data on how intermittent fasting (with or without high insensitivity internal training) affects weight gain (fat accumulation) and changes to blood tests (such as fasting glucose level, lipid profiles etc).
The study utilized 90 mice (male and female) that were fed a 60% fat / 30% sugar diet for 3 months prior to the 3 month study. Once they were bulked up, the weight from the “control” group of mice was recorded. It was used a baseline measurement for comparison with the other experimental groups for the end of the study (limitation #1 of the study). The assessment of caloric intake per mice was not calculated. The intake of each group was collected and averaged amongst the mice (limitation #2).
The experimental groups were broken down into: mice that just performed intermittent fasting (IF), only high-intensity interval training (HIIT), IF+ HIIT, and nothing (control).
The IF group had 2 (non-consecutive) days a week that were fasting (75-100% reduction in caloric intake) followed by allowance to eat as tolerated on non-fasting days. This group was essentially on a severe energy restriction schedule.
The HIIT group was on a significant energy expenditure schedule. The mice would participate in brief spurts of vigorous exercise (80-90% breathing capacity) followed by longer / lower intensity activity that included passive recovery phases. The model was essentially 20 seconds “on,” and 40 seconds “off” with increasing intensity intervals over 6-8 cycles. This required more “up front energy” that continued to burn after the exercise was completed while in the “recovery phase.”
The combination group (IF + HIIT) spent 2 days of intermittent fasting with 3 days of HIIT. After fasting, the mice would have 24 hours of recovery before completing their exercise.
The control group did neither IF nor HIIT.
After 3 months of intervention, the measurements below were collected from each of the experimental groups:
- Body weight
- Fat mass
- Fasting glucose
- Fasting insulin levels
- Insulin sensitivity
- Lipid profile (HDL, LDL)
[On average, regardless of IF/ HIIT / IF+ HIIT, the mice consumed the same average intake of calories on non-experimental days of the week].
The results of the study are below:
- Male mice demonstrated the greatest improvements in body composition changes, glucose control, and lipids levels compared with female mice
- Despite consuming a diet high in sugar and fat, male mice who participated in IF +/- HIIT had statistically significant less weight gain, stable lean muscle mass, and lower LDL levels
- Female mice had significantly lower triglyceride levels in the IF + HIIT group
- Both IF genders had worsening fasting glucose markers
What Does This Mean For You?
Obviously, mice are not the same as humans, so the effects of human hormones and metabolism may differ between the two species; especially in females. It is interesting to note how building 3 days of high intensity workouts into our weekly routine (even for just 10 minutes at a time) can affect our body’s composition and ability to prevent fat weight gain.
For men, two non-consecutive days a week with a light caloric intake can potentially amplify changes in your body composition, glucose control, and cholesterol levels.
Additionally, the mice in the study were fed a high fat / high sugar diet. By eating a clean, minimally processed diet, I think it would be safe to assume that the results one would find from the study could have an even greater impact.
You can find the study through PubMed HERE.