If you’re wondering whether the low FODMAP diet will help you lose weight, let me be clear from the start: this isn’t a weight loss diet.

The goal of the low FODMAP diet is not to cut calories, but to temporarily remove fermentable carbohydrates that may be triggering your IBS symptoms.

If you need help with the low FODMAP diet (including recipes and clear process steps) check out my Ultimate Low FODMAP Diet Guide. 

When the low FODMAP diet feels like a weight loss plan

One of my previous clients assumed they would lose weight during the low FODMAP phase because it felt so restrictive—similar to past experiences with calorie-controlled diets.

This client found the food rules emotionally challenging. For them, being on “a diet” of any kind meant dealing with food guilt, constant planning, and even disappointment when she hadn’t lost weight, despite all her efforts.

That’s why it’s so important to understand the true purpose of the low FODMAP diet and set realistic expectations. This client felt very cheated when after all this work they didn’t actually lose any weight, even though she was doing everything right.

Why weight loss is not recommended on the low FODMAP diet

If you are looking to lose weight, my advice is do one thing at a time. From working with hundreds of clients I recommend addressing your digestive issues and then focus on weight loss.

Trying to do both at once can backfire. Here’s why:

• It’s too complicated – Following the low FODMAP diet is difficult, I’m not going to lie! It requires a lot of thought at first to check you’re not inadvertently eating higher FODMAP foods, and it’s not a very intuitive diet. Adding on further controls in terms of energy intake will be adding to your workload and could reduce your chances of sticking with the plan.
• You need to keep up your energy levels – If you drop your calorie intake and this leaves you lacking in energy, or affecting your sleep then this could mess up your FODMAP challenges. 

Why some people lose weight on the low FODMAP diet

So, will the low FODMAP diet help me lose weight? Well, yes, some people find they do lose weight when on the low FODMAP diet, but not necessarily because they’re trying to. Common reasons include:

• Smaller portions of carbohydrate-rich foods – As part of controlling the portions of high FODMAP foods many of my clients find they eat fewer carbohydrates (e.g. pasta and bread) and focus more on protein. 
• More awareness of portion sizes – Once you start checking the recommended serving sizes of some foods you might realise you were eating more than the recommended portion sizes for certain foods. 
• Cutting back on snacks – If you’re avoiding high FODMAP snacks like biscuits or crisps in the office, your overall energy intake might drop without you realising. If you feel like you’re missing out on too many social occasions bring some food with you so you can at least eat something with the others. 

While these changes can support weight loss, they’re a side effect—not the goal of removing high FODMAP foods.

But what about if you don’t want to get any smaller?

How to avoid unintentional weight loss on the low FODMAP diet

Some of my clients are underweight or already in a smaller body and are worried about losing more weight during the low FODMAP process. After all, you’re removing some foods so naturally there could be a change in your energy intake. 

This can happen due to:

• Over-restriction out of fear of triggering symptoms

• Eating too little during the FODMAP elimination and reintroduction phases

• Ongoing gut symptoms like nausea, bloating or pain affecting appetite

Here are some tips on avoiding weight loss during the low FODMAP restriction and challenge phase. 

• Increase the size of your protein portions at every meal. Animal sources of protein contain no FODMAPs so you can freely eat eggs, meat, fish and seafood. Vegetarians can include tofu, nuts, and low lactose dairy.
• Try eating 4-5 smaller meals instead of 3 large meals. Make the additional meals a proper meal, not just biscuits, crisps, but actually adding protein and healthy fats. This allows you to space out the FODMAP rich food, but increase your calories throughout the day. 
• Concentrate on low FODMAP wholegrains such as rice, quinoa, oats and potatoes. 
• Don’t skip healthy fats – A small amount of fat at each meal can add energy and help with nutrient absorption. Try nut butters, butter, small portions of nuts or seeds. Small amounts of avocado can also be tolerated by most people. 

I’ve written a longer blog post about how to gain weight with IBS

It’s tricky to change your diet if you have IBS, so please don’t go it alone. If you want to help just ask to arrange a discovery call, and we can talk about working together in the 3 month Gut Reset.

Listen to my podcast episode 50 about gaining weight.