Some people with IBS are in the very difficult position of needing to gain weight, yet having to limit food choices and portion sizes to avoid setting off their IBS symptoms. Believe me, people who are underweight get plenty tired of cracks about how lucky they are. It isn't funny; it can be scary to be underweight, and even harder to gain weight for some people than it is for the rest of us to lose it.
High calorie intake may be needed for weight gain, or to support high levels of activity such as training for a marathon or working at a demanding physical job. One memorable patient of mine was a tall, slightly underweight 18 year old male college student who had a very physical summer job, played soccer for a couple hours after work most nights, and had a lovely mom who prepared mostly vegetarian food (read: beans) at home, and plenty of it. He had to consume thousands of calories a day to support his calorie needs--how can someone with IBS do this without blowing up!?
It is helpful to recall that oils do not contain any FODMAP carbohydrates. Oils contribute 9 calories per gram, versus only 4 calories per gram from protein and carbohydrate. So the #1 weight gain strategy for FODMAP sensitive individuals or those on the elimination phase of the diet is to EAT MORE HEALTHY FATS, such as olive oil, canola oil, any kind of nut or seed oil. I think coconut oil is over-rated as a "healthy fat" but it is low in FODMAPs, so go ahead and eat more of it if you must gain weight for your health and if your doctor or dietitian agrees. I know, I know, you've always read that people with IBS shouldn't eat too much fat, but is that really true for you? Try it and see for yourself, before you limit your fat intake unnecessarily, based on over-generalized advice. You might be able to tolerate more healthy fat than you think. There is a huge difference between a tablespoon of olive oil (13.5 grams of fat) and a Bloomin' Onion (134 grams of fat--ouch). Just because greasy fried foods make you feel sick, doesn't mean you can't try some olive oil on your salad, or drizzle your roasted veggies liberally with it. If you have to limit fat intake because of another medical condition, seek the help of a registered dietitian to help you plan your weight gain.
Many high-protein foods are low-FODMAP source of calories for weight gain, again because they are automatically low in both sugars and fibers (potential FODMAPs). If you need to gain weight and you don't have any other health issues (such as kidney stones or kidney disease) that would make it inadvisable to eat more protein, you might try bigger portions of the following foods:
- Lactose-free milk
- Lactose-free yogurt or kefir
- Lactose-free cottage cheese
- Aged Cheeses
- Puddings and custards made with lactose-free milk, eggs, and granulated sugar
- Firm or medium tofu (Unseasoned. Not silken.)
- Tempeh (This is a fermented soybean food. Make sure it is unseasoned.)
- Seitan (Seitan is a protein food made of wheat gluten. Must be home-made without onion or garlic powder to be low in FODMAPs.)
- Canned, drained chick peas or lentils
I advise you to try these things for yourself to see if you tolerate them. Don't over-restrict based on one-size-fits-all advice that people with IBS shouldn't eat red meat, for example. And don't worry that eating more protein is only for people who want to lose weight--it might seem that way from some things you read, but it's not true.
Note that alternative milks such as almond milk and rice milk are not good sources of protein compared to cow's milk.
Most people can get enough protein from food, but If you are into protein powders, see my post on FODMAPs and Protein Powders.