GLP-1 Fiber Calculator

Why the target follows your calories

The dietary-guidelines basis for fibre is 14 g per 1,000 calories. That is the whole calculation: your intake divided by a thousand, multiplied by fourteen. The familiar flat figures of 25 g for women and 38 g for men come from the same rule applied to a general adult intake — reverse them and you get about 1,800 and 2,700 calories respectively.

Which is exactly why they mislead on a GLP-1. If appetite suppression has taken you to 1,400 calories a day, a 25 g target is not a stretch goal, it is a different diet from the one you are eating.

A worked day at 1,600 calories

The 22 g target sounds like a lot until you place it. One cup of raspberries is 8 g. Half a cup of cooked lentils is another 8 g. A cup of broccoli adds 5 g. That is 21 g from three items, and the lentils carry protein at the same time. An apple with the skin on (4.5 g) or a tablespoon of chia (5 g) closes any gap.

Note what did the work there: whole foods that bring water, potassium and volume along with the fibre. Reaching the same 22 g from a single scoop of powder is arithmetically identical and functionally different.

Why constipation is so common on these medications

GLP-1 medications slow gastric emptying — that delayed transit is part of how they blunt appetite, and it is also why constipation appears among the common gastrointestinal adverse reactions on both the tirzepatide and semaglutide labels. Add the fact that eating less automatically means eating less fibre, and the problem compounds itself: your calories fall, your fibre falls with them, and transit was already slower.

There is a real trade-off here that most fibre advice skips. Fibre is filling, and on a suppressed appetite your stomach space is the scarcest thing you have. If a large salad means you cannot finish the protein on the plate, it has cost you more than it gained. Clear your protein floor first, then reach the fibre target with foods that deliver both — lentils, black beans, and other legumes are on the list above for that reason.

The trap: adding fibre fast, or adding it dry

Two failure modes, and they are the reason people conclude fibre made things worse. Going from 10 g to 25 g in a day reliably produces gas, bloating and cramping, so build up over a couple of weeks rather than in one shop. And fibre works by holding water — increasing it without also increasing fluid can leave you more constipated, not less. Every gram you add needs something to drink alongside it.

If you use a fibre supplement rather than food, the fluid rule matters more, not less. Check it with your pharmacist first, particularly if you take other medicines, since timing around other tablets can matter.

Where this target does not apply

A calorie-based fibre goal assumes you are eating normally and have no condition that restricts fibre. Low-residue or low-fibre diets are prescribed for good reasons — active inflammatory bowel disease, known strictures, some post-surgical recovery — and in those cases your clinician's instruction replaces this number entirely.

Fibre is also not a treatment for everything the gut does on a GLP-1. It does not help nausea, and it will not resolve constipation that has become severe. Constipation lasting more than a few days, or accompanied by vomiting, severe abdominal pain or a swollen abdomen, is a reason to contact your prescriber rather than to add another serving of bran.