You might feel it’s impossible to gain weight with IBS symptoms thwarting your efforts. If you’ve been on strict elimination diets, or missing meals due to your sensitive digestion you may have lost weight without intending to.

Unexpected, or undesired weight loss can be more prevalent with IBS-D, people who have a diarrhoea predominant type of IBS, because the transit time of food doesn’t allow for proper absorption of food.

How do you know if you need to gain weight with IBS?

Underweight is considered a BMI of less than 18.5. Your BMI is adjusted for height and gender, but it does not take into account muscle mass, so it’s important to look at body composition as well as the BMI score.

Muscle weighs more than fat, so consider whether you’re a healthy BMI, but with a very low body fat.

If you’re underweight it can lead to problems with your immune health, and can put you at greater risk of fertility issues, infections, osteoporosis and age related muscle wasting (sarcopenia). Being underweight seems to be more of an issue for men than women.

People with IBS tend to lose weight due to restrictive diets aimed at eliminating trigger foods. Unfortunately the list of foods can become very long, and leave you without a well balanced diet.

Is your weight loss unexplained?

If you’ve recently lost weight without meaning to, especially if it’s been rapid, it’s important to get checked over by a doctor.

Think about how much weight you’ve lost, and in what time period.  A significant weight loss over a shorter time period may be of more concern.

The NHS suggest a loss of more than 10kg body weight in 3 months would be a red flag for further investigation, or 5-10% of your body weight. 

Get your doctor to rule out other conditions

Weight loss could be related to something else, such as Inflammatory Bowel Disease, Coeliac Disease, an overactive thyroid, or cancer so speak to your GP or gastroenterologist to rule these out.

Some people have a naturally fast metabolism, or are constantly moving which burns off more exercise.

Or is your weight loss explained by your diet?

Sometimes it’s easy to see how what you’re eating could cause weight loss. You may be restricting your food variety, or total amounts. Common restrictions are:

• low fat diet due to issues digesting fats or bile acid malabsorption
• Dairy free diet – avoiding all cheese, cream, milk etc
• finding protein hard to digest
• low FODMAP long term diet
• combination of dairy free, gluten free, soy free, no sugar etc.

Maybe you’re skipping meals to avoid bloating or stomach pains. Maybe you’re only eating a small amount at each meal because you quickly feel full. 

Get your digestion sorted first

If you are able to resolve some of the ongoing digestive issues, you may find it easier to absorb more nutrients from your food. Work with a registered, qualified nutritional therapist to identify the root causes of your digestive symptoms. Contact me for a quick chat about my nutrition packages to see how I can help you.

How to gain weight when you have IBS or SIBO

Ultimately you need to eat more calories than you burn every day. It’s important to do that slowly and using healthy foods that support your body. My top 7 tips are below, but essentially it boils down to:

Add calories

• You should start with adding around 500 calories per day to start seeing an increase in your weight. 

Add volume

• You may need to eat more often, or eat bigger portions. This will be even if you feel full, bloated, or nauseous.

Could your fear of the consequences of eating be holding you back?

You may feel nervous about eating different foods, or more food in total because you’ve been so used to restricting your diet. When taken to an extreme some people develop an eating disorder called Avoidant Restrictive Food Intake Disorder. 

This is understandable because you’ve been trying to find a way to manage your symptoms. But when it leads to weight loss, or nutrient deficiency then psychological support can help.

A counsellor or therapist training in disordered eating may be useful to you if this resonates with you.

Related Post – IBS and Disordered Eating – Food Anxiety

1. Regular meal times can help you add body weight

Aim to eat regularly through the day, and don’t miss meals. When you eat in an erratic pattern you may end up stressing your digestion even more by cramming more food into a shortened eating window. 

Skipping meals may lead to more weight loss, or becoming deficient in certain nutrients.

What about the overnight fast? 

Don’t worry about the overnight fast that’s often suggested (by people like me) to help in SIBO. When we don’t eat over night our digestion can rest, and the migrating motor complex gets to work cleaning the small intestine.

Getting back to a healthy weight is much more important than this period of not eating. Including a small snack in the evenings can be a good way to add calories to your day. 

2. Small frequent meals can help weight gain with IBS

If you fear stomach cramping, or pains because you need to eat more food, then try to break it down into smaller meals.

Extra meals don’t need to mean unhealthy snack food choices. Choose foods that add key nutrients like healthy fats, fibre and protein to your diet.

You may find it helpful to stick to low FODMAP foods when trying to add new foods to your diet. Each person is so different in what they react to with IBS and SIBO, but experimentation is important. 

3. Increase your fats to gain weight

Fats contain 9 calories per gram, compared to 4 calories for protein and carbs. This means you can opt for high fat foods to increase your overall calorie intake. Some people will struggle with fat digestion so build up slowly to see where your tolerance lies for oils and fats.

If you can manage lactose containing foods, include full fat milk, eat hard cheeses. You can even play around with adding cream to your diet.

Healthy plant based fats are avocados, nuts, seeds, coconut oil, olives.

But what about FODMAPS?

Well not everyone with SIBO or IBS reacts to every kind of fermentable, starch, and our tolerance to certain foods can increase over time. So test out how you get on with small amounts of avocado, or nuts and build up from there.

Oily fish are also a healthy source of calories and the omega 3 helps with anxiety and mood issues. 

4. Increase protein intake

Protein is a building block for muscles, so it’s important to eat enough every day. In order to gain weight it’s estimated you need around 1.5-2kg of protein a day for every kilo of body weight. So if you’re 60kg you could need to eat up to 100g of protein. That is a large amount of protein every day so you’ll need to break it down and think about each meal.

Should I use a protein shake to gain weight? 

• Consider a protein shake if you struggle to eat enough food. You can get vegan protein powders, or whey based shakes. Add these to your diet on top of food. 
• If you’re using shakes try to sip them slowly rather than downing it, that can make you feel sick or overly full. 

Healthy protein sources are chicken, fish, seafood, eggs, nuts and nut butters, seeds, tofu, pulses and beans.

5. Improve your appetite

Take time to focus on your meals so you’re relaxed and ready to digest a meal.

Address nutrient deficiencies

Zinc deficiency may cause a loss of appetite so if you never feel hungry consider if this could be a factor for you. Zinc is found in meat, fish, whole grains like brown rice, wheat and nuts and food sources are best.

You can trial a supplement, but don’t take one long term as it can compete for update with other minerals. 

Move more to feel more hungry

Although it’s counterintuitive sometimes doing more exercise can help stimulate your appetite. 

Spend some time thinking about appetite

Some people with IBS never feel hunger. Loss of appetite is common in ARFID, or it may indicate you’ve minimised your connection to your body through years of trying to ignore your digestive symptoms. 

6. Don’t drink at mealtimes

Liquid can displace space for food so glugging down lots of drink at each mealtime might be making you eat less than you need.

It’s ok to sip on water to help your meal go down, but avoid drinking huge glasses each meal. 

7. Get quality sleep

Being sleep deprived can interfere with our body’s repair processes.

• We build muscle overnight whilst resting.
• Anxiety can be worse when we’re tired, so aiming for 8 hours of sleep is important when you’re starting to change your IBS diet.
• Gut symptoms may be worse when you’re tired, including experiencing more pain.

If you have been struggling to gain weight for a while and would like some targetted help from me, an IBS nutritionist, please email about setting up a discovery call so we can chat about what you need.