Carb Cycling for Peak Metabolic Function

Hormones at Play

Hormones, a major muscle building component largely influenced by diet and lifestyle, are the notes that make up the overall tone of your health and well-being. And if hormones are the individual notes in this equation then think of your thyroid as the conductor. The thyroid regulates hormone production related to your metabolism which in turn determines how quickly and efficiently you are able to utilize your fat reserves.

The ultimate goal of carbohydrate cycling is to have optimal fat burning capacity by strategically manipulating the thyroid’s response to macronutrient intakes.

The key hormones that regulate metabolism are thyroxine (T4 for short), and the more potent triiodothyronine or T3. In this article, we will discuss hormones that influence metabolic function, some of the common pitfalls of carbohydrate restriction and how carbohydrate cycling will help you overcome them.

Kick-Starting Your Metabolism

Ever hear someone complain they got saddled with a slow metabolism by their mother’s side or they just gain fat faster than skinny people? We’ve all had a friend with these excuses for not reaching their goal weight or ideal body image. It is a defeatist mentality to fall into the trap of thinking you do not have any recourse against nature or heredity. All too often environmental influence is overlooked in favor of the status quo excuse that is the dreaded “slow metabolism”.

While it is true, some people are clearly at a metabolic disadvantage to start, a fact that is often overlooked is that your metabolism is not only one-directional. You can speed up your metabolism too! The important piece to know is that your metabolism is largely the result of your thyroid which is influenced by environmental factors like sleep, exercise and diet. What many people fail to realize is that dieting, and carbohydrate restriction in particular, can have a deleterious effect on your thyroid function.
In order to get that thyroid humming along, you’re going to need to do a few things to give it that kick in the rear it so richly deserves. One of the first steps is to start by signaling your body it needs to shape up or ship out. In other words, serious change needs to happen and the only thing which will do this is compound movements with heavy weights at high intensity and adequate carb fuel to do so.

Once you’ve ramped up exercise intensity, it’s time to simultaneously begin to tackle the all-important dietary component, specifically keying in on your macronutrient ratios. Carbohydrate intake has been proven to stimulate T3 production more favorably than other macros.

Concentrations of T3 were increased when carbohydrate was isocalorically substituted for fat in the diet [….]It is apparent from these studies that the caloric content as well as the composition of the diet, specifically, the carbohydrate content, can be important factors in regulating the peripheral metabolism of thyroid hormones.6

T3 supports numerous functions in the body but for our purposes we are primarily concerned with its effect on rate of metabolism. T3 increases the basal metabolic rate meaning calories required for normal body processes when your muscles are at rest I.e. your ability to burn calories when sitting on your backside. This is huge because over time an increased basal metabolic rate (BMR) chips away at fat reserves and calorie surpluses with more persistence than any amount of cardio could touch. Why you ask? Well because unlike our gym routines, BMR never takes a day off!

Avoiding Hormonal Havoc

The thyroid is connected to the very most primal part of the brain linked to human survival. In times of food scarcity, the thyroid tells the body to slow up, conserve and hunker down for the long haul whether it be famine or a brutal winter. The thyroid is also utterly indifferent to your fitness goals; it responds as it has for hundreds if not thousands of years prior to the advent of supermarkets and protein powders.

Many main stream diets rely heavily on carb restriction which often works great in the short term but eventually brings your metabolism to a screeching halt. The reason for the slowdown is multifaceted but one of the key hormones at play is cortisol. Cortisol has been shown to be elevated on low carbohydrate diets.

Twenty-four hour urinary cortisol excretion, a hormonal measure of stress, was highest with the very low-carbohydrate diet. Consistent with this finding, Stimson et al1 reported increased whole-body regeneration of cortisol by 11β-HSD1 and reduced inactivation of cortisol by 5α- and 5β-reductases over 4 weeks on a very low- vs moderate-carbohydrate diet. Higher cortisol levels may promote adiposity, insulin resistance, and cardiovascular disease, as observed in epidemiological studies. 2,3,4

High cortisol is also proven to compete with and largely inhibit the production of Testosterone. In short, you do not want to stress your body into a catabolic state. A recent study from the University of Texas found:

According to research, chronically elevated cortisol levels can produce impotence and loss of libido by inhibiting testosterone production in men. 5

Severely restricting carbohydrates for prolonged periods will do this which is why you will need high carb days to offset metabolic slow down. Carbohydrate fits in like the last piece of a jigsaw puzzle here by allowing you to ramp up your metabolism while still being able to enjoy the fat-burning benefits of short term carb restriction.



1.Stimson RH, Johnstone AM, Homer NZ,  et al.  Dietary macronutrient content alters cortisol metabolism independently of body weight changes in obese men.  J Clin Endocrinol Metab. 2007;92(11):4480-4484PubMedArticle

2.Adam TC, Hasson RE, Ventura EE,  et al.  Cortisol is negatively associated with insulin sensitivity in overweight Latino youth.  J Clin Endocrinol Metab. 2010;95(10):4729-4735PubMedArticle
3.Holt HB, Wild SH, Postle AD,  et al.  Cortisol clearance and associations with insulin sensitivity, body fat and fatty liver in middle-aged men.  Diabetologia. 2007;50(5):1024-1032PubMedArticle

4.Purnell JQ, Kahn SE, Samuels MH, Brandon D, Loriaux DL, Brunzell JD. Enhanced cortisol production rates, free cortisol, and 11beta-HSD-1 expression correlate with visceral fat and insulin resistance in men: effect of weight loss.  Am J Physiol Endocrinol Metab. 2009;296(2):E351-E357PubMedArticle


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