Carbohydrates Intake: Quantity

Carbohydrates Intake: Quantity

The 'minimum effective dose' approach employed in the last Protein article offered a slightly different perspective on calculating macro-nutrient needs.

This week, I'm tackling a more controversial topic: Carbs.

In keeping with the previous theme, this article will analyse carbohydrate requirements from a biological perspective - in other words, I'm not looking at observational studies looking to establish correlation between carbohydrate intake and performance, just what you need to function normally.

A few assumptions that are worth keeping in mind:

1) for the sake of argument, I will assume that those reading this are not in a 'fat-adapted' state (brought on by following a ketogenic diet)

2) and, the analysis is based on an average weight, resistance training individual. No 95+kg bodybuilders, or people doing marathon 1.5-3hour training sessions!


The Approach:

Carbohydrates fuel one of the body's base energy storage mechanisms: glycogen - a structure made of multiple glucose molecules chained together.

The body stores glycogen in a few different places, the two main locations being in the Muscles, and in the Liver.

The glycogen stores in the muscles, of particular interest to us, help fuel any form of exercise requiring glycolysis (glyco - glycogen, lysis - break down). This encompasses any effort ranging from 10 seconds to 2 minutes.

The brain is also a major user of carbohydrates (in the form of glucose).

Using this basic information, it is possible to calculate base glucose requirements for an exercising individual.


Some (very) basic maths/biology:

Let's start counting:

- the brain uses, on average, 120g of glucose per day.

- The average person stores around 300g (same reference as above) of glycogen in their muscles, and, during high intensity exercise (lasting ~30-45 mins), can use roughly 30% of it (1, 2), which equates to approximately 100g.

- Glucose is required for many other reactions in the body, however, this can be supplied by the liver (~100g of stored glycogen), and the kidneys (through gluconeogensis - the making of glucose form other nutrients - namely fats/proteins). So we need not worry about this!


Some concrete numbers:

Having calculated the above, the average individual's basic needs for carbohydrates are:

On a training day: 220g

On a rest day: 120g



These are 'minimum effective dose' numbers, and they assume a normal diet (and by this I mean a diet where a person is not purposefully restricting carbohydrate and protein intake to trigger ketosis). they are not a maximum intake.

120g of carbohydrates only represents 480 calories, and 220g represents 880 calories. By no means a huge amount!!

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