Loose stools in the first fortnight

Loose stools in the first two weeks are common enough that they should be expected rather than feared. They usually settle. Knowing the difference between adaptation and something that needs attention is the useful skill.

Four things happen at once

Fat arrives in the small bowel faster than the bile supply can emulsify it. Bile salts are recycled, and the pool is finite; a sudden jump from 80g of fat a day to 200g exceeds it, and the excess passes through. The result is pale, loose, floating stools that are urgent rather than painful.

Bile acids reach the colon in greater quantities than before, because there is less plant fibre to bind them and carry them out. Bile acids stimulate water secretion in the colon, which produces a loose stool that comes with little warning.

Water and sodium shift in the first week as glycogen falls, and gut transit speeds up with the change in volume and composition of what is eaten.

Whatever else you changed arrives at the same time. Black coffee on an empty stomach, magnesium, sugar free gum, a protein powder, a new supplement. Most people change five things and then blame the beef.

What usually fixes it

Spread the fat out. Three meals with 60g of fat each is a different experience from one meal with 150g.

Step the fat up over two weeks rather than going straight to ribeye and butter on everything. Start with 20% fat mince and add the extra butter in week two.

Stop drinking large volumes of water with meals. A pint with food speeds things along.

Check the supplement shelf. Magnesium citrate and oxide, sugar alcohols such as sorbitol and maltitol, and some vitamin C powders all loosen stools on their own.

Take dairy out for a week if you were eating cheese, cream or milk in quantity. Lactose is the commonest single cause of a loose stool that people blame on the meat.

Give it ten to fourteen days before you conclude anything. The bile adaptation in particular takes that long.

What not to do

Do not take an anti-diarrhoeal medicine to get through a work day without also fixing the fat intake, because you will be back where you were by the evening.

Do not drop to zero fat. Loose stools on a very high fat intake do not improve by removing fat altogether; they improve by spreading it out.

Do not add a fibre supplement in week one, which produces gas and a different problem.

When it is not adaptation

Most people who get this get it for three to ten days and then it stops. What should send you to a GP or to 111:

Blood in the stool, or black tarry stools.

A fever, or feeling generally unwell rather than just inconvenienced.

Loose stools that continue past two weeks without improving.

Waking at night needing to go, which is a pattern that ordinary dietary change does not usually produce.

Unintentional weight loss.

Signs of dehydration: dark urine, dizziness on standing, a dry mouth, tiredness that is out of proportion.

Vomiting that stops you keeping fluids down.

If you have Crohn's or colitis, any change in bowel habit should go through your specialist team before you experiment further.

The one sentence version

Expect loose stools for a week, spread your fat out, check your supplements, give it a fortnight, and treat blood, fever, night waking or two weeks of no improvement as a reason to stop guessing.