You should avoid any type of fatty food, such as foods that are high in saturated fats and sugars. These increase your risk and are harmful to your body.
This site offers great information on gastric foods http://www.livestrong.com/article/411294-foods-to-avoid-for-gastric-stomach/ also try http://www.faqs.org/oc/Overcoming-Digestive-Problems/Foods-to-eat-foods-to-avoid.html
This website http://www.mayoclinic.com/health/gastric-bypass-diet/my00827 gives you the diet you should follow for gastric bypass surgeries. It even tells you which foods to avoid.
Your doctor or dietician will 9/10 chances tell you what foods are good for you and what foods you should avoid after the surgery. Stick to whatever it is they recommend for you especially being that everyone is different as far as the body.
You should try to avoid sweet foods such as chocolate
Avoid aspirin, alcohol, vitamin E and certain medications before you think about having a tummy tuck operation. Your doctor might also want you to not eat certain foods before the operation.
Foods to avoid... gaseous foods-dark leafy green veggies, beer, carbonated liquids, dairy, corn odorous foods-fish, eggs, asparagus, garlic, beans, and dark leafy green veggies
Make sure that you ask his doctor directly what foods he should eat in his plan. He can plan on recovering from this surgery in 2-3 days, depending on the doctor's decision.
You will be advised to avoid solid foods after your surgery for around two days. It is generally advised to avoid the following foods, popcorn, nuts and seeds, breads, in the first weeks after surgery.
He should try to avoid foods such as nuts and seeds. As well as other foods such as popcorn, dried fruits carbonated drinks, breads, meats that can be tough as well as things like celery that can be stringy.
Foods you should eat before and after having the gastric bypass surgery are high in protein but low in calories, fats and carbohydrates. Some doctors may need you to be on a full liquid diet for a few weeks. Foods that you should eat after the surgery are liquids, soft foods and then solid foods when the doctor says. You can have six small healthy meals a day.
Any foods that have a high sugar level content or junk foods are the foods that you should avoid. Have fresh fruit and vegetables every day to keep you , or concentrated in class, work etc.
You should avoid high calorie foods because they will make you gain weight. You should avoid acidic foods because they will give you indigestion.