Get to know the Glycemic Index (GI). It rates carbohydrates according to their effects on blood sugar. Carbs are ranked on a scale of one to 100+ (glucose is 100). Low-glycemic foods, as you would imagine, have a lower number. This means they do not spike your blood sugar, and are generally healthier for you. High-glycemic foods have a higher number; they quickly elevate your blood sugar, and are not as healthy for you. In general, I like to stay with foods that have a GI rating under 60.
Most popular diets are considered fad diets. There is no clear definition for what constitutes a fad diet. Merriam-Webster defines a fad as "a practice or interest followed for a time with exaggerated zeal." Fad diets often promise quick results with a short time commitment. Long-term success requires permanent changes in behavior, diet, and activity.