Metabolic Flexibility Using Protein

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.

What Does Research Show?

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).

Unless you go bat$hit crazy or have any current kidney issues, higher protein intake is unlikely to cause any issues. Up the dietary protein if you are looking to increase your performance and improve your body composition via metabolic flexibility.   

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. Why? 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


1: Storlien L, Oakes ND, Kelley DE. Metabolic flexibility. Proc Nutr Soc. 2004 May; 63(2):363-8. Review. PubMed PMID: 15294056.

2: Kelley DE, Goodpaster BH, Storlien L. Muscle triglyceride and insulin resistance. Annu Rev Nutr. 2002;22:325-46. Epub 2002 Jan 4. Review. PubMed PMID: 12055349.

3.  Baum JI, Layman DK, Freund GG, Rahn KA, Nakamura MT, Yudell BE. A reduced carbohydrate, increased protein diet stabilizes glycemic control and minimizes adipose tissue glucose disposal in rats.  J Nutr. 2006 Jul;136(7):1855-61.

4. Krezowski PA, Nuttal FQ, Gannon MC, Bertosh NH. The effect of protein ingestion on metabolic response an oral glucose in normal individuals. Am J Clin Nutr 1986; 44:847- 56.

5. Samaha FF, Iqbal N, Seshadri P, Chicano KL, Daily DA, McGrory J, Williams T, Williams M, Gracely EJ, Stern L. A low carbohydrate as compared with a low-fat in severe obesity. N Engl J Med 2003; 348:2074-81.

6. Walker-Lasker DA, Evans EM, Layman DK. Moderate carbohydrate, moderate proteinweight loss diet reduces cardiovascular disease risk compared to high carbohydrate, low

protein diet in obese adults: A randomized clinical trial. Nutr & Metab 2008, 5:30-9.

7. Boden G, Sargrad K, Homko C, Mozzoli M, Stein PT. Effect of a low-carbohydrate diet on appetite, blood glucose levels, and insulin resistance in obese patients with type 2

diabetes. Ann Intern Med 2005; 142:403-11.

8. Gannon MC, Nuttall JA, Damberg G, Gupta V, Nuttall FQ. Effect of protein ingestion on the glucose appearance rate in people with type 2 diabetes. J Clin Endocrinol Metab

2001; 86:1040 –7.

9. Gannon MC, Nuttal FQ, Saeed A, Jordan K, Hoover H. An increase in dietary protein improves the blood glucose response in persons with type 2 diabetes. Am J Clin Nutr.

2003; 78:734-41.

10.  Parker B, Noakes M, Luscombe N, Clifton P. Effect of a high protein, high monounsaturated fat weight loss diet on glycemic control and lipid levels in type 2 diabetes. Diabetes Care 2002; 25:425–30.

11.  Sakamoto K, Aschenbach WG, Hirshman MF, Goodyear LJ. Akt signaling in skeletal muscle: regulation by exercise and passive stretch. Am J Physiol Endocrinol Metab. 2003 Nov;285(5):E1081-8. Epub 2003 Jul 1.

12.  Reynolds TH 4th, Bodine SC, and Lawrence JC Jr. Control of Ser2448 phosphorylation in the mammalian target of rapamycin by insulin and skeletal muscle load. J Biol Chem 277: 17657–17662, 2002

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.

Share This Article:

Share on facebook
Share on twitter
Share on email
Share on tumblr

Close X

For Our Free
Product Educational
Video Series

Discover important, basic product information, the best way to take a supplement and the science behind our top selling products, all in our
FREE Product Education Video Series.

Scroll to Top