FODMAP stacking, explained

FODMAP stacking is when several foods that are each low FODMAP at the amount you eat add up to a high FODMAP meal. A food’s “low” amount is worked out for one serving of that food on its own, but your gut gets the whole plate at once. So it’s worth looking at the meal as a whole, not just at each food.

Why FODMAPs add up

FODMAPs cause symptoms through the amount that reaches the gut. In a placebo-controlled trial, people with IBS who were given rising doses of fructose and fructans had more symptoms as the dose went up.^[1] The body doesn’t know which food the FODMAPs came from: fructans from oats and fructans from banana are the same fructans.

The low amounts on food lists don’t account for this. The research cut-offs that decide whether a food is low were set by looking at the FODMAP content of a typical serving of each food.^[2] They tell you about one food at a time. Two or three foods near their limit in the same meal can go over, even though none of them would on its own.

A worked example

Every number here comes from Fodmi’s food data. Take a slice of toast with banana:

• 40 g of spelt sourdough. It stays low up to 52 g; above that, its fructans rise. This slice uses about three quarters of its low amount.
• 50 g of firm banana. It stays low up to 95 g; above that, its fructans rise too. This is about half its low amount.

Each is low on its own. Both carry fructans, though, so together they come to about one and a quarter low servings of fructans: more than one sitting should hold. The plate is no longer low, though every food on it is within its own low amount.

The fix is easy: have the banana as a snack a few hours later, swap it for a fruit low in fructans, such as blueberries, or use less of each.

How to plan around stacking

• Look at the whole plate. Most meals mix one or two foods with some FODMAPs and plenty with almost none, such as rice, potatoes, meat, fish, eggs and oil.
• Watch foods with the same group. Wheat, onion, garlic and some fruit all carry fructans. Two of them in one meal stack faster than two foods from different groups.
• Spread foods across the day. A food that would tip one meal over can usually go in another meal or a snack.
• Use the food pages. Each food page shows the amount up to which that food stays low. Foods near their limit leave less room for anything else.

Stacking matters most in the strict first phase. In the reintroduction phase you learn which groups you tolerate and how much, and the reintroduction guide explains how. A dietitian can help you plan meals that fit your own limits; the British guideline advises that a trained dietitian supervises the diet.^[3]

How Fodmi checks meals

When you log a meal in Fodmi, it adds up the FODMAPs from every food in it, group by group, and shows whether the meal as a whole is low, alongside each food’s own result. Each food counts as a share of its own largest low serving, and the shares of foods with the same group add up; at one whole serving’s worth, the group is no longer low. Every meal in our meal plan and our low FODMAP breakfasts passed the same check. It is a guide, not medical advice.