"Funny turns": What they aren't and what they might be.

Sometimes, doing a large amount of high-intensity exercise while on a ketogenic diet can result in a "Funny turn", i.e. a weird feeling which may include sweating, dizzyness & feeling faint.

The good news is that it's harmless, provided you don't faint, fall and hurt yourself. Stop and sit/lie down until the feeling passes. So, what's happening?

What isn't happening is a Somogyi rebound. A Somogyi rebound only happens when too much insulin is injected and it's bad because it results in hyperglycaemia.


Did you know that there is insulin, insulin and insulin? According to Insulin: Degradation, "It has been estimated that an insulin molecule produced endogenously by the pancreatic beta cells is degraded within approximately one hour after its initial release into circulation (insulin half-life ~ 4–6 minutes)". According to Insulin: As a medication, injected insulin lingers in the blood for hours for fast-acting and days for slow-acting. This makes an overdose of injected insulin dangerous, as it can linger for long enough to cause fatal hypoglycaemia unless medical help is obtained.

What might be happening is this: On a ketogenic diet, muscle glycogen stores are "trickle-charged" using blood glucose. High-intensity exercise burns muscle glycogen at a very rapid rate. See It's all in a day's work (as measured in Joules). Muscles can burn carbs at a rate of 4g a minute.

If muscles run low/out of glycogen, muscle cells become exquisitely sensitive to insulin as glucose importing processes are up-regulated. There is only about 4.5g of glucose in the blood at any given time, topped-up by the liver and burned by the brain & red blood cells at a rate of less than 4g an hour (if keto-adapted). If muscles start to draw in 4g of glucose a minute, blood glucose can vanish very quickly.

As dropping dead due to running for your life on very little or no food is bad, the body has several mechanisms for raising blood glucose very quickly.

From Blood Glucose, Insulin & Diabetes, "When BG falls to about 3.3mmol/L, the pituitary gland kicks-in and secretes ACTH (adrenocorticotropic hormone) which stimulates the release of cortisol from the adrenal cortex. Cortisol further stimulates gluconeogenesis in the liver. When BG level falls to about 2mmol/L, the pituitary secretes GH (Growth Hormone) which has an anti-insulin effect." At a BG level of about 2mmol/L you feel really weird, so you stop exercising.

So why is it harmless? Glycogen-depleted & exquisitely insulin-sensitive muscles act as a natural blood glucose limiter because they draw in glucose so readily. There is no hyperglycaemia.

This also reduces the "Dawn Phenomenon", another plus point for low-carb diets for diabetics.

See also Can very-low-carb diets impair your mental faculties.