Mike T Nelson, CSCS, MSME, PhD
Athletes are constantly looking for ways to do 2 main things: 1) increase performance 2) improve body composition.
Metabolic flexibility is the ability of the body to use fat as the main fuel during low intensity exercise / rest and to also use carbohydrates to fuel intense training (1,2)
If you can increase metabolic flexibility, you can increase the use of fat without impairing the ability to use carbs during weight training / high intensity interval training sessions; thus, maximizing both aspects.
How do you do it? There are several ways, but here is one that I have used for years that works really well for almost every athlete.
In a wicked cool study by Baum JL et al. 2006 showed that adding more dietary protein in place of carbohydrates resulted in better glucose and insulin management (3).
The high protein group used 35% carbs, 35% protein, 30% fat. Before the pubmed Ninjas get their fruit-of- the-looms all in a bunch, yes, this was a rat study. I know, I know, we are not large weight-lifting rats, but there is a wealth of data in humans that supports this conclusion (3-10).
Your body’s response to primarily carbohydrates (and some protein) is normally biphasic with a fast and slow component of insulin release. Not only can the total amount of insulin be different, the release pattern can also be different – and messed up by too many carbohydrates dumped into a non-receptive environment (such as type 2 diabetes).
From the study by Baum JL et al. 2006 (3):
“The high-CHO diet group required a highly responsive endocrine system to modulate the large swings in glucose metabolism from the food-deprived to fed periods….. increased emphasis on peripheral disposal of dietary carbohydrates in skeletal muscle and adipose tissue.
Rats consuming a reduced CHO diet with increased protein reflect minimal diurnal variations in blood glucose or endocrine regulations…. minimize the need for postprandial glucose clearance by adipose tissue.“
In English – the rats in the high-carb group needed to be super metabolically flexible to handle the massive influx of carbs or they were potentially going to have some issues. The furry ones in the higher protein group did not have to “work as hard” to get rid of all the extra glucose.
It Must Be the Calories!
Yes calories matter and the laws of physics still apply, but many times in these types of studies, one arm of the study has many many more calories than the other, making it an unfair fight. This time it was isoenergetic (fancy word for the same amount of calories in each group) clocking in at about 4,500 kcal.
Physical exercise activates protein synthesis via phosphorylation (activation) of p70S6K in a pathway that is dependent on mTOR. Akt was also higher in the protein group. Both p70S6K and Akt are highly associated with increases in protein synthesis and bigger muscles (11, 12). Adipose Akt was higher though in the higher carb group, showing more activity in fat tissue to dispose of the higher carbohydrates.
Remember, high amounts of glucose in the blood stream can be toxic if left unchecked so the body does everything it can to get them the heck out of there; even if that means stuffing it in fat cells.
In similar study by Devkota, from Dr Layman's group again (13), showed an increase in fatty acid synthesis in the higher-carb rat group too.
Increased satiety . . . You feel full longer.
Increased muscle repair (increases protein synthesis–taking proteins and stuffing them into muscle tissue for bigger and stronger muscles).
For those looking for more practical human data:
“High-protein diets most often are associated with muscle hypertrophy and strength, but now also are advocated for weight loss and recovery from intense exercise or injuries” (14)
More protein has a more “even” effect on blood glucose regulation and helps muscle repair.
Isn't Protein Dangerous?
Unless you go bat$hit crazy or have any current kidney issues, higher protein intake is unlikely to cause any issues (14).
Up the dietary protein if you are looking to increase your performance and improve your body composition via metabolic flexibility.
Dr. Mike T Nelson
PhD, MSME, CSCS
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13. Devkota S1, Layman DK. Increased ratio of dietary carbohydrate to protein shifts the focus of metabolic signaling from skeletal muscle to adipose. Nutr Metab (Lond). 2011 Mar 4;8(1):13. doi: 10.1186/1743-7075-8-13.
14. Tipton KD. Efficacy and consequences of very-high-protein diets for athletes and exercisers. Proc Nutr Soc. 2011 Mar 7:1-10.