Loading up on sweets and crisps won’t sustain you over hours of hard work, and will almost certainly result in a crash. This is particularly harmful to productivity as your brain burns more glucose when trying to exert self-control. Eating foods that slowly release energy over time is better for your health and productivity. Think unprocessed, whole foods and a lunch with a balance of protein, veg, fat and carbs.
Source: learn.filtered.com