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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.

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. 

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.

Get your digestion sorted

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.

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How to gain weight

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.

You may feel nervous about eating different foods, or more food in total because you’ve been so used to restricting your diet. This is understandable because you’ve been trying to find a way to manage your symptoms, and you may need to work on your emotional approach to food as part of gaining weight.

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

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.

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

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 new foods, but don’t rely on this as each person is so different. 

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 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.

Increase the protein

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.

  • 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.

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

Improve your appetite

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

Zinc deficiency may cause a loss of appetite so if you never feel hungry consider if this could be a factor for you.

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.

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.

Hi I'm Anna Mapson, registered Nutritionist (mBANT, CNHC). I help people with IBS, gut health and digestive issues.

I can help you to:

  • understand your digestion better, so you recognise your triggers
  • eat a well balanced diet, with tasty meals that are simple to prepare
  • develop healthy, sustainable habits for life

“Anna is amazing! I feel totally transformed"

To find more about 1:1 nutrition consultations or my group membership see my IBS Diet support page