I essentially live on oatmeal because of food sensitivities.
No, oats will NOT make you fat.
What you put on them may, but plain oatmeal won't.
I lost weight when I switched from wheat to oats.
Don't know about barley, however barley is a good lower carb grain. I make beef barely soup with it and that's essentially all I use it for.
There's something about wheat though, that makes me pork up almost instantly. I am NOT gluten sensitive nor do I have celiac. Whatever it is, wheat makes me fat.
I use barley in my vegetable soup. A favorite of all who partake.
Unless there's some leftover pizza, I'll take oats for breakfast. Love the taste so much, I don't put anything on them except water. No milk, fruit, or sugar, just water. Hungry after sunset -- oats! I weigh about 97 pounds, nothing to worry about when one is just 60 inches high. Fixing a bowl of oats in the microwave takes 45 seconds, another benefit :) Eggs are more nutritious but I haven't the patience in the morning. You have to keep an eye on eggs.
I have hypoglycemia (opposite of diabetes) so blood sugar is very low in the morning and only what I eat (controlled carbs) can control that. So for breakfast I regularly have eggs (omelet style) with only fresh spinach inside, and a dusting of dried basil on top (because I love the taste of basil). A couple of times a week I instead have plain oatmeal (Bob’s Red Mill whole grain rolled oats) with about a half cup of blueberries on top. That seems to satisfy the blood sugar problem and builds up to normal by 10:00. And if I don’t have time for lunch some days, I’m not hungry, and grabbing an apple will do. My downfall is loving breads and pasta at dinner time……sigh
Wheat makes your gut leak. Much of the toxins from your leaking gut get encapsulated in abdominal fat as a defense mechanism. The toxins not captured also contribute to systemic inflammation which damages just about every critical system in your body.
https://pubmed.ncbi.nlm.nih.gov/25734566/
Wheat would be banned for human consumption in any rational civilization.