Salaam. This is my veiwpoint; We must struggle with our nafs all our lives, the dinner table being part of our lives. In my opinion, and i am no doctor, but what i understand from the nature of food, the nafs and the example of the Messenger (s.a.w) your doctor is wrong that you need to eat a "lot" for better health IF this is his general opinion. However, i dont know your specific health and lifestyle so I cant say he is wrong in your case. Our stomach is the size of our clenched fists. A third of that needs to be filled at the BEST of times. (from the hadith of a third food, third water and third air whenever you eat) The stomach is elastic, hence, the larger the stomach, the larger the third needed to fill it. Also fasting on Mondays and Thursdays may help explain why "some days" one doesnt feel hungry. If you reduce your stomach to its normal unelasticated size, Jihad on the nafs at the table also include education and understanding where our foods come from. You must learn about foods. Learn about what enters the stomach. Where it is made, how it is made, who is making it, what farming methods are they using, are they modifying the foods genetically, are they using battery farming, are the animals that constitute the food product treated well, artificial sugars in drinks, water sources, containers our foods are packaged in, life plastic foams and plastic wrappers. If you are consuming products with high sugars, that increase hyperactivity, and decrease conentration in prayer and in studies, then its not only the sugars which are a problem its the product itself. To me, these are the true meaning of halal, not just - Chicken McBurger, cool Halal logo and bismillah before you eat it ? We need very little food to survive. Food for 2 is enough for 4, sometimes food for 2 is enough for 8. Subhanallah we live in an age, where food for 1 is sometimes enough for 20 ! Allah hu Alim, Allah is Al-Hakim and Al-Haqq.