Proponents of high-carbohydrate diets advocate that carbohydrate-restricted diets have a negative impact on testosterone levels, on insulin, IGF-1, as well as other hormones.
However, most of the research has been made on subjects who restricted carbohydrate intake for a few days. That’s not enough for a person to get keto-adapted (efficiently burn fat to produce energy, instead of using carbohydrates for energy).
It takes from at least two weeks to up to a couple of months for the body to be fully adapted and efficient on metabolizing fat as the primary source of energy.
Think about it, there are a lot of enzymes involved in the process of metabolizing fat and these have to increase in number to support the new metabolism. It takes some time.
On the other hand, Jeff Volek and Steven Phinney have researched carbohydrate restricted nutrition and its impact on health and physical performance for more than 2 decades.
Jeff Volek along with other researchers has conducted a study on 20 normal-weight men which have been divided into two groups of 12, respectively 8 individuals. The study lasted for 6 weeks.
The Two Groups
The first group of 12 men shifted from their diet consisting of ~48% carbohydrates (% of total calories per day) to a diet consisting of ~8% carbohydrates. Their protein intake shifted from ~18% to ~30%, while the fat intake increased from ~32% to ~61%. So, they moved to high-fat-very-low-carb nutrition.
The second group, consisting of 8 men, did not change their dietary intake patterns. Thus, they were mostly consuming a diet which consisted of: ~58% carbohydrates, ~16% protein, and ~26% fat. They had a high-carbohydrate diet throughout the whole period of 6 weeks.
The high-fat-very-low-carb group:
1 subject – sedentary
5 subjects – regular aerobic exercises for 2-4 times/week for 20-60 minutes each session.
6 subjects – aerobic exercises 3-5 times/week for 15-90 minutes/session + resistance training 2-6 times/week for 45-120 minutes/session
They were basically maintaining the same exercising routine they had before starting the experiment.
The control group:
– they maintained the same routines in terms of exercising and eating as they had before the experiment.
Results – Body Composition
Results were collected at weeks 0, 3, and 6 (they used DXA scans). Here are the body composition results:
As you can see in the table, the low-carb group has lost a significant amount of body fat (-3.4kg) and they slightly increased their lean mass (+1.1kg). In my n=1 experiment I noticed the same changes (lost 5% of body fat and slightly gain lean mass).
Conversely, there were no significant changes in the control group.
Results – Hormonal Changes
The control group did not show any significant changes in any hormones.
The high-fat-very-low-carb group has shown:
– decrease in serum insulin levels (-34.2% at week 6).
– increase in total T4 (+10.8%)
– increase in free T4 index (+12.5%)
– no significant changes in: testosterone, SHBG, IGF-1, cortisol, glucagon, and T3 uptake.
Key Take Away
Insulin is a hormone that has a powerful inhibitory effect on lipolysis (fat breakdown). Moderate to high-insulin levels do not promote fat break-down. So, insulin is like the guardian of fat tissue. Low levels of insulin in the context of a keto-adapted person is a powerful promoter of fat break-down because fat becomes the primary fuel of the body. The body does not rely on glucose for energy anymore.
Conversely, cortisol, thyroid hormones, as well as glucagon are stimulators of lipolysis .
There are four other studies that the authors of the research consider to be done on keto-adapted individuals, which are relevant to the carbohydrate-restricted regimen where the subjects have been keto-adapted for a period of several weeks. See them below.
Again, studies made on carbohydrate-restricted diets that follow subjects for only a few days are far to be called relevant. This study shows that there are no negative effects on hormonal levels when humans are adapted to a very-low-carbohydrate diet. I’m very optimistic that other studies of this kind will follow up.
L.E.: Here’s a good study from 2014.
1. Stephen Phinney and Jeff Volek – The Art and Science of Low Carbohydrate Living
2. Volek, J. S., Sharman, M. J., Love, D. M., Avery, N. G., Scheett, T. P., & Kraemer, W. J. (2002). Body composition and hormonal responses to a carbohydrate-restricted diet. Metabolism, 51(7), 864-870.
3. Benoit, F. L., Martin, R. L., & Watten, R. H. (1965). Changes in Body Composition During Weight Reduction in Obesity Balance Studies Comparing Effects of Fasting and a Ketogenic Diet. Annals of internal medicine, 63(4), 604-612.
4. Phinney, S. D., Horton, E. S., Sims, E. A., Hanson, J. S., Danforth Jr, E., & Lagrange, B. M. (1980). Capacity for moderate exercise in obese subjects after adaptation to a hypocaloric, ketogenic diet. Journal of Clinical Investigation, 66(5), 1152.
5. Young, C. M., Scanlan, S. S., Im, H. S., & Lutwak, L. (1971). Effect on body composition and other parameters in obese young men of carbohydrate level of reduction diet. The American journal of clinical nutrition, 24(3), 290-296.
Photos: here and here