What Works and What to Avoid

By Dr. Sherry Nabil Rizk

Eating all the right foods but still facing digestive problems and weight control issues? The key may not be what you eat, but how you eat it. Our bodies produce digestive enzymes to help us break down, assimilate and utilize the foods we consume, but often we mix things together in meals that end up confusing our systems.

Different enzymes are required for different types of food, and the result when too many are called into play at one time can have adverse effects. You will be surprised to see how many common combinations and eating habits can be culprits.

1. Fruit should be eaten alone:

When you combine fruit with foods that take longer to digest such as meat and starches it stays too long in your stomach and starts to ferment. It is best eaten half an hour to an hour before a main meal, never directly after a meal. When fruit is eaten alone on an empty stomach before a meal, it prepares the digestive tract for what’s to come.  Melons in particular should be eaten alone as they decompose very quickly in the stomach and are almost sure to cause trouble if eaten with other foods. A separate meal should be made of them so that they are quickly passed out of the stomach, and can be enjoyed for their nutritional benefits.

2. Avoid having proteins and starch in the same meal:

Proteins and starch need different enzymes and different levels of acidity to be digested. When eaten together, your body is forced to make a choice to digest protein but not starch. This results in undigested starchy food undergoing fermentation and decomposition, which leads to unpleasant end products. The protein will putrefy and the carbohydrate will ferment. The result is gas and flatulence in the system. Top tip – Combine protein or starch with non-starchy vegetables. If you do have to mix animal protein and starch, add leafy green vegetables to minimize the negative side effects.

3. Mixing two concentrated types of protein:

In general protein/protein combinations are not recommended. One single concentrated protein per meal is easier to digest and won’t require as much energy. Concentrated proteins take a long time to break down, tax the digestive system and deplete energy.

4. Avoid eating carbohydrates and acidic foods in the same meal:

Tomatoes should ideally not be combined with any starchy food. They may be safely eaten with leafy vegetables and fat foods. The combination of citric, malic and oxalic acids found in tomatoes, (which are released and intensified by cooking), is very antagonistic to the alkaline digestion of starches in the mouth and stomach. They should not be used on salads in a starch meal. Tomatoes are considered acidic and are not advised to be mixed with starchy carbs such as pasta. Adding dairy to this already difficult combo in the form of cheese sets you up for digestive problems. Try pasta with pesto or grilled vegetables instead.

5. Fats with Proteins:

This combination is one of the worst offenders in our daily diets. Fats require bile salts from the liver and gall bladder to break down; mixing them with other digestive chemicals can cause distress and slow digestion. Fatty acids lessen the activity of the gastric glands, the gastric juice, and lower the amount of pepsin and hydrochloric acid. While we should all make an effort to reduce to reduce consumption of harmful trans-fats and saturated fats we do need a certain level of fat in our diet. Use small amounts of fat — particularly, organic, unrefined oils like olive or coconut — when cooking vegetables, grains, and protein. Protein fats like avocados, seeds, and nuts should be combined only with non-starchy vegetables. It helps to include a raw leafy green vegetable when eating fats.

6. Liquids with Meals:

Any liquid in your stomach dilutes the enzymes your body needs to digest proteins, carbohydrates, and fats. This covers drinking water or juice during your meal or tea directly after eating. Water goes through the stomach in about 10 minutes while juice takes 15 to 30 minutes.  So drink as much water as you wish at least 10 minutes before sitting down to eat, then after eating wait about an hour to have any liquid.

7. Starch and sugar together:

Combining starch with sugary foods is a bad way to eat carbohydrates. When sugar is eaten the mouth quickly fills with saliva, but no ptyalin is present. Ptyalin is essential for the digestion of starch. If the starch is disguised with sugar, jellies, jams, or syrups the taste buds are confused, and carbohydrate digestion is impaired. Monosaccharides and disaccharides ferment more quickly than polysaccharides, so are prone to ferment in the stomach while awaiting the completion of starch digestion.

8. Time counts:

Some foods take a long time to digest while others move through the body relatively quickly.  Bear in mind that on average, fruits take 30 to 60 minutes to digest; vegetables, grains, and beans take one to two hours; cooked meat and fish take at least three to four hours; and shellfish takes four to eight hours. When you combine foods with different digestion periods you may face discomfort because your digestion isn’t as efficient. If you combine fruit with a slower digesting protein it sits in the stomach hours longer than it would on its own. As a result, the sugars in the sweet fruit ferment, leading to bloating and gas. If food rots in the stomach or intestines instead of being efficiently digested, we don’t absorb all of its nutrients.

Any time you have fermentation or putrefaction, it can create gases that are toxic and even carcinogenic. These toxins in the system may also cause fatigue, irritability, headaches, and foul breath initially, then later may result in colitis, inflammation, constipation, arthritis, and high blood pressure.

9. All in good order:

The order in which you eat various foods can also affect your body’s chemistry. Different categories of foods require different digestive enzymes to break them down, and those enzymes come from different parts of the body. Amylase and lipase come from the mouth and the small intestines digest carbohydrates and fats. Pepsin comes from the stomach and other enzymes from the pancreas to help break down proteins. Bile salts come from the liver and gallbladder to emulsify fats. And enzymes in the small intestine digest the sugars in fruits.


Try the following eating schedule:

Morning meal:

The least concentrated foods, in the greatest amount. Fruit makes a great start to the day.

Middle of the day:

More complex foods, but in a smaller amount than your first meal. Starchy carbohydrates will give you energy to burn.


The most concentrated foods, but in the smallest amount. This is when you can go for foods that take longest to digest, proteins work well.


Dr. Sherry Nabil Rizk is a Professor at Cairo University. She is also available as a nutritionist and body shaping consultant by appointment at In Shape Clinic.