Your brain needs 50g of glucose a day

Adapted from Richard Feinman’s Nutrition in Crisis 

We have all heard NHS dieticians and diabetologists telling us that we will die of brain failure or get severe brain damage when we go on low carb diets because the brain needs 130g of glucose a day.

We will typically remind them that the glucose does not need to be ingested since our livers are perfectly able to manufacture well over 130g of glucose a day, the process called gluconeogenesis.

Richard Feinman is a cell biologist and he has an even finer retort.

The 130g of glucose a day necessity was discovered by George Cahill. This was the amount of glucose that a brain uses in normal nutritional states. It is indeed the case that this glucose can be ingested or manufactured in the liver or both.

Under starvation conditions however, the brain will only use 50g of glucose a day.  In starvation, the utilisation of ketone bodies becomes more important for brain function.

Unfortunately, nutritionists picked up on the 130g of glucose a day message and have been repeating it ever since. Cahill is reported to have said that by the time he was aware of the simplified but inaccurate message, it was too late to stop it.

Thus, it is not always true that you need 130g of glucose a day for brain function and it is never true that this must be from dietary carbohydrate.

So, if you get the old chestnut thrown at you, you know what to say now!