Anybody having trouble digesting grains should definately try soaking, sprouting or fermenting them first. Most traditional societies treated their grains in this way, it's only a relatively new thing to just eat them straight (and boy doesn't it show with the rates of grain intolerances!)
I do better off gluten but will occasionally (a few times a year) eat fermented oats, sprouted spelt bread or sourdough spelt/rye. These processes actually reduce the gluten content... not great for full blown Coelics, but can be all that's needed for gluten intolerance of lesser severity.
For gluten free grains I eat quinoa, buckwheat, amaranth and millet. I cannot eat rice, gives me gut issues and is mostly starch and not much nutrition anyway. I make a bread by freshly cracking quinoa, buckwheat and amarath and then add warm water and whey and ferment the flour mix over a day or two. Improves the nutrition and the digestability.
Coconut flour is also an alternative to use. It is basically 90% fibre or so, and can mimic grains. However I don't do too great with this and most ME patients will probably find that the huge amount of fibre and small traces of leftover fructose (naturally occuring in coconut) will result in gut disturbance. But if you can tolerate it it's a good filling grain free low carb alternative.
Honestly though, the whole grain things is just 'feedlot' nutrition aka. the food pyramid. There's nothing you're going to get from grains that you couldn't get from meats, organ meats, dairy, eggs, vegetables etc. It's more a cultural thing and what you're used to. Overall I think reducing grain intake is the best idea. You don't have to eliminate them entirely, but one serving a day max.... start deconstructing the idea that a grain is part of almost every meal.
Also as Danny said - people who are slim and ill should not go low carb. High protein/high fat and low carb diets are great for healthy people, overweight people, or average weight people, but people who are slim AND sick will find that without the extra fat buffer that eating carbs gives, they will only waste away their muscle tissue under stress/infection. It's not safe.
So the diet for weight loss = no refined sugars what so ever. 5-7 pieces of fruit a week. No more than one serving of grain/legume a day. Limit starchy vegetables to 1-2 servings a week. Liberal amounts of high quality meats, eggs, dairy, non-starchy vegetables etc.
For weight gain, people want to be consuming very high quality proteins and optimise the absorption by not drinking water for 30 mins before and 90 mins afterward (small sips okay). Hydrocloric acid supplements or digestive enzymes can help. Or you can consume herbal bitters, or any kind of food that increases bile production, 15 minutes before your big protein meals. This is all for muscle growth. For fat growth (important for very sick and slim people, you need a buffer... something for your body to eat away before your muscle in event of bodily stress). Starchy vegetables are incredibly helpful in this scenario - sweet potatoes, potatoes etc. They should be eaten with liberal amounts of high quality butter, extra virgin olive oil, cheese, cream, coconut cream etc (your choice) to slow down sugar absorbtion though. You want them to make you gain fat but not cause you daily trouble by destabilising your blood sugar levels.
People who need to gain some fat can also have smoothies with raw honey, and lots of bananas and cream (or coconut cream).
I support low carb eating on the whole however in the special circumstance of people with low muscle mass and very low body fat, starches, natural sugars and some grains are important to include. They DO cause fat gain which is desirable and healthy for some people.