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Ketosis and Fasting: Do BCAAs Break a Fast or Ketosis: Thomas DeLauer

Ketosis Overview

Ketosis is a metabolic state that occurs when dietary carbohydrates are in such low quantities that your body must rely almost exclusively on fatty acid oxidation and ketone metabolism

A traditional ketogenic diet sees you reduce carbs to around 5% of total energy intake with a maximum carb limit of 50g per day.

Simply put, a ketogenic diet results in your body using and burning fat, rather than carbs, for fuel (energy)

BCAA’s Overview

Amino acids are the building blocks of protein. Branched chain amino acids (BCAAs) are so called because of their structure, which includes a “side chain” of one carbon atom and three hydrogen atoms.

BCAAs are the only amino acids not degraded in the liver.

All other amino acids are regulated by the gut and the liver before being circulated elsewhere in the body.
This means that dietary intake of BCAAs directly influences plasma levels and concentrations in muscle tissue (Layman DK 2003). Interestingly, BCAAs are burned for energy (oxidized) during exercise, so they’re also an important exercise fuel.

So this poses the question…. If it can be used as fuel, can it break a fast?

BCAAs, however, head directly into the bloodstream. This means that dietary intake of BCAAs directly influences plasma levels and concentrations in muscle tissue

There are three BCAAs: leucine, isoleucine, and valine

BCAA supplementation may reduce muscle soreness, accelerate recovery, promotes muscle protein synthesis and supports fat loss (1,2)

Ketosis and Insulin

Insulin’s primary purpose is to regulate the metabolism of fats and carbohydrates. The digestive system breaks down carbohydrates, such as sugars and starches, into a molecule called glucose.

Insulin allows cells in the body absorb glucose so your body can use it for fuel, ultimately lowering levels of glucose in the blood stream

Ketosis and Insulin

Ketosis will take place when the body needs energy and there is not sufficient glucose available for the body.

This happens when the body is lacking insulin and blood glucose levels become high.

BCAAs can Spike Insulin

Studies have shown that branched-chain amino acid supplementation increases insulin levels and concentrations of FFAs

Leucine, specifically, stimulates glucose uptake for up to 45 minutes (3,4)

Insulin and Ketosis Study

Despite there being some benefits to supplementing BCAAs, it may not be wise to do so while in a ketogenic state

In one study, a man voluntarily fasted for 50 days.

His ketones were high (14 mmol/l) and he was injected with insulin (around 0.1 IU/kg, so around 7-8 IU).

For 30 min, his ketones and blood sugar dropped and there was a massive uptake of ketones by the brain and ketone production was halted.

However, within 30 min his ketones started shooting back up

In short, an insulin spike can kick you out of ketosis, albeit temporarily, as insulin clearance is seemingly fast (5)

BCAAs While in Ketosis (Increase in circulating BCAAs)

In one study dietary replacement of carbohydrate by fats were studied in six healthy subjects, which was preceded and followed by a 3-day period of balanced diet.

During the ketogenic diet, levels of free fatty acids, glycerol and 3-hydroxybutyrate rose significantly and glucose levels decreased by 16.5 +/- 3.2%

The hormonal pattern switched towards a catabolic mode with a fall in insulin levels (-44.0 +/- 6.3%) and a rise in glucagon concentration (+39.0 +/- 10.4%).


The average levels of gluconeogenic amino acids (alanine, glutamine, glycine, serine and threonine) were reduced by 8-34% while those of the branched chain amino acids increased by more than 50%.

Concluded that a ketogenic diet may result in an increase of circulating BCAAs within the body – so supplementing with BCAAs may be even less necessary while in ketosis (6)


1) All About BCAAs | Precision Nutrition. (n.d.). Retrieved from http://www.precisionnutrition.com/all-about-bcaas

2) Ten Benefits of BCAAs | Poliquin Article. (n.d.). Retrieved from http://main.poliquingroup.com/articlesmultimedia/articles/article/1088/ten_benefits_of_bcaas.aspx

3) The Ketogenic Diet and Insulin Resistance | Ruled Me. (n.d.). Retrieved from https://www.ruled.me/the-ketogenic-diet-and-insulin-resistance/

4) Ketosis – What is Ketosis, Effects of Ketosis and Ketosis Levels. (n.d.). Retrieved from http://www.diabetes.co.uk/blood-glucose/ketosis.html

5) Hyperlipid: Neuron fuel and function. (n.d.). Retrieved from https://high-fat-nutrition.blogspot.com/2014/07/in-comments-following-previous-post.html

6) Hormonal and metabolic changes induced by an isocaloric isoproteinic ketogenic diet in healthy subjects. – PubMed – NCBI. (n.d.). Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/6761185