OP, you’re getting somewhat conflicting diet advice on this thread. As others have said, it’s best to get professional guidance on that question—and keep in mind that everyone’s different, so what works Aunt Jane (or some semi-anonymous poster on CC) won’t necessarily work for your husband. But as someone who has lived with diabetes in the family for a long time, I’ll add my two cents. First, as others have noted, type 2 diabetes is caused by insulin resistance, which causes the body not to process blood glucose properly. Body fat can cause or contribute to insulin resistance, but it’s not the only cause. In fact, unexplained weight loss is often a symptom of the onset of type 2 diabetes because insulin resistance prevents the body’s cells from getting sufficient glucose, so they begin to
metabolize body fat and muscle in an attempt to compensate. So I’m not surprised that your husband lost weight before being diagnosed as pre-diabetic.
I don’t think anyone’s completely figured out how to beat insulin resistance—if they had, we wouldn’t have so many type 2 diabetics. In pre-diabetics who are overweight or obese, the usual advice is to lose weight, as this may help reduce insulin resistance, but in a person who is already slender and physically active, it’s more challenging. You probably don’t want to dramatically reduce caloric intake. So then it’s a question of where the calories are coming from.
You can limit or prevent glucose spikes by reducing total carb intake, changing the composition of carbs you’re taking in, and eating balanced meals at regular intervals while avoiding snacks. Foods with a high glycemic index that can cause glucose to spike are those containing sugars and simple starches, e.g., soda, fruit juice, white potatoes, white pasta, baked goods, and any processed foods containing white flour and/or high-fructose corn syrup. Whole grain bread and pasta have a lower glycemic index—they contain dietary fiber, which is good in its own right, and it takes the body longer to break down the complex carbs in whole grains, so you’re less likely to get a high glucose spike, but they’re still carbs, so avoid eating too much. Most diabetes experts recommend that you eat whole fruits, with the caveat that you eat them in moderation, and choose wisely—apples and pears will give you a lower glycemic load than grapes, raisins, or dates… I’d also resist the temptation to offset the calories lost from reduced carbohydrate intake by increasing calories from fat. A number of studies have found that dietary fat can heighten insulin resistance, quite independently from body fat. That’s why many type 2 diabetics tend to have trouble with Chinese food—it’s not the carbs but the oils used in cooking that heighten short-term insulin resistance and may lead to a glucose spike The American Diabetes Association recommends that you limit both fat and carbs (especially but not only high-glycemic carbs) by increasing consumption of vegetables, especially leafy green vegetables. Their “plate method” recommends that you make vegetables half of each meal, leaving one quarter for carbs and one quarter for low-fat proteins. An exception: some studies have found that the oils in fish can actually reduce insulin resistance.
Keep in mind, though, that essentially all you’re doing here is preventing glucose spikes. Whether that reverses the underlying insulin resistance is less certain, but it could help prevent a mild case of insulin resistance from blossoming into full-blown type 2 diabetes, And finally, if it does develop into type 2 diabetes, it’s not the end of the world. Many type 2 diabetics lead long, active, and relatively healthy lives by managing their diabetes through diet, exercise, and medication. You don’t want to go there if you can avoid it, but if it happens it can be managed.