Hi Chad. I was just wondering if it would be worth the effort to workout first thing in the morning in a fasted state, instead of working out right after I’ve had breakfast? Would I burn more fat doing my training while fasting? I’m trying to get the most bang for my buck with the effort I’m putting in. Any input would be appreciated! Thanks in advance.
Hi Lisa. According to well documented research there definitely is inherent benefits associated with fasted training versus training on a full, or even semi-full stomach. One of the most noteworthy studies I read was conducted by De Bock, et al (2005) and Cluberton, et al (2005). The purpose of their study was to determine if fasted training offered any advantages to a trainee in terms of fat metabolism, glucose tolerance, and insulin sensitivity.
To conduct this study they recruited a group of young, healthy males who were relatively lean and also active. The subjects of this study averaged 3.5 hours of exercise per week. Two weeks prior to the study, various tests were conducted to ascertain body composition, fitness, diet, and certain metabolic values. The subjects were divided into 3 groups, 2 of which followed the exact same diet and training regimen. The only thing different was that one group trained in a fasted state and the other group did not. The 3rd group followed the same diet as the other 2 groups, but didn’t do any exercise during the study which I personally think is a moot point, but I’m not a researcher so perhaps they can see something between the lines that I can’t see.
Anyways, the group doing fasted exercise was labeled group F, the group doing non-fated exercise was labeled group C, and the group engaging in zero exercise was labeled the CON group (short for control group).
Group F and C
Both the F group and the C group engaged in two, 60 minute and two, 90 minute long supervised training sessions each week, always between 6:30 am and 9:00 am. The exercise sessions consisted of a combination of cycling and running. Training intensity was adjusted for each subject and set to 70-75% VO2Max for cycling and 85% VO2Max for running. Ninety minutes prior to training, the C group received a high carbohydrate breakfast that was 675 calories, 70% carbohydrates, 15% fat, and 15% protein. Additionally, during exercise they also drank a beverage that contained 1 gram of maltodextrin per kilogram of body weight.
The F group was given the same breakfast and maltodextrin rich beverage as the C group, but later on in the middle of the afternoon. The CON group was the given the same breakfast and maltodextrin drink, but did not do any exercise. The overall diets of the subjects consisted of 50% fat, 40% carbohydrates, and 10% protein— very similar to the diet of the average American. The subjects were also given a 30% surplus of calories above the amount required to maintain their stable body weight and composition.
The study lasted 6 weeks. Upon completion, new tests were conducted to determine changes in body composition, fitness, diet, and certain metabolic values. I won’t even bother going over the results of the CON group. Needless to say, nothing good happens in your body when you sit on your butt all day and stuff your face.
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So, I’ll just focus on the results of groups C and F…
Glucose tolerance and insulin sensitivity:
Both of these values go hand in hand. Insulin sensitivity is closely related to glucose tolerance and vise versa. They are both significant values when it comes to metabolic health. The F group clearly experienced improved glucose tolerance and insulin sensitivity. The C group did as well, but to a much lesser degree than the F group.
Glucose transporter type 4 is a protein responsible for insulin regulated transport into muscle cells. In the F group GLUT4 increased by 28%, but only by 2-3% in the C group. This is part of the reason why subjects in group F experienced better glucose tolerance and insulin sensitivity results. GLUT4 is activated by AMPK, which increases when glucose levels are low, which is what the circumstances are training in a fasted state. That being said, it would make sense that AMPK levels would have to be higher to yield an increase in GLUT4. That was exactly the case, as 25% increase of AMPK was also noted among the subjects in group F.
There are two values that measure fuel utilization efficiency, known as citrate synthase and HAD. Interestingly these values were the same among both group F and Group C. However, there were two other values that were measured which are significant to glucose and fat metabolism. These values are known as FAT/CD36 and CPT1. These values did increase by a staggering 30% in group F, whereas group C did not experience any increases of these values at all.
Even though the subjects were consuming a surplus of 1,000 calories or more, group F only gained 0.7 kilograms which is relatively insignificant. It’s worth mentioning that some of this weight gain could possibly be attributed to increased muscle glycogen stores. How did group C do? Those subjects ended up gaining 3.5 kilograms, double the amount of group F, despite doing the exact same amount of exercise and consuming the same amount of calories and macronutrients as group F!
I want to remind you that these changes transpired after just a 6 week period. Looking long term, you can get an idea of just how much impact fasted training could have over time. According to research, the differences could be quite profound.
Based on the scientific evidence, I would say fasted training would definitely be worthwhile if you’re able to tolerate it. In my personal experience, training in a fasted state is much easier and more efficient if you take 5-10 grams of BCAAS prior your workout and then again immediately following your workout.
I hope that this information provides the direction you were looking for. I wish you all the best of success with your health and fitness goals!
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