Executiveassistant:
Which is better to add more of to get a bigger belly?
Be careful with both - especially sugar. Contrary to popular belief, sugar makes you fatter than fat does. However, this fat tends to be visceral (organ) fat. This says nothing of the risk for tooth decay and diabetes.
It's best to go for a diverse, high-calorie diet. At least get a mix of healthy and unhealthy foods. That way, you can get fatter for longer periods of time.
