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While some people argue that the body is unable to digest properly if foods are eaten in the wrong combinations, there’s no evidence to back that theory up

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My naturopath told me that I should eat fruit by itself, or an hour before eating a meal. I was told I won't get all of the nutrients in fruit if I eat it in combination with other foods. Is this true?

These days, my usual breakfast consists of oats, kefir and raspberries. I eat them all mixed together; I don't eat the berries first. And I may even eat an orange soon after finishing my lunch. Does this mean that my body is shortchanged vitamin C, folate, potassium and other nutrients contained in my berries and citrus fruit? Simply because I eat them with – or in close proximity to – other foods? Hardly. Here's why.

The premise of food combining

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Proponents of "food combining" argue that the body is unable to digest foods properly if they're eaten in the wrong combinations. Getting it wrong, they say, can lead to bloating, gas, heartburn, weight gain, malnutrition and even disease.

The modern version of food combining was created by U.S. physician William Hay in the early 1900s. Hay, after following his plan for three months, lost 30 pounds and improved his health. In the 1980s, popular variants of the Hay Diet included Judy Mazel's The Beverly Hills Diet and Harvey and Marilyn Diamond's Fit for Life.

(For the record, a food-combining diet has been the subject of only one randomized controlled trial, which found no evidence that it improved weight loss or health above and beyond a low-calorie balanced diet.)

One of the tenets of food combining is that fruit should be eaten only on an empty stomach.

Since fruit is digested more quickly than protein and starchy foods, you'll realize its maximal nutritional value only if you eat it by itself. Eat it 30 to 60 minutes before a meal, or two to four hours after a meal, food combiners advise.

If you eat fruit in combination with other foods, though, it will get "trapped" in your stomach and start to "rot" before it can be digested and its nutrients absorbed. You'll also feel digestive distress.

Another common food-combining rule: Avoid eating protein (e.g., meat, poultry, fish, eggs, tofu) and starchy foods (e.g., bread, pasta, grains, winter squash, potato) together in the same meal.

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The theory goes that since protein and carbohydrates require different enzymes to be broken down, enzymes that operate at different pH levels in the gut, eating them together will "cancel out" or neutralize their digestive enzymes and prevent proper digestion of either food. (pH is a measure of acidity or alkalinity.)

Digestion 101

The proposed rationale behind food combining goes against the physiology and biochemistry of human digestion. Our digestive tract is, in fact, exquisitely equipped to effectively digest and absorb mixed meals.

It's true that protein is partially digested in the acidic stomach and that carbohydrates are broken down into their building blocks in the alkaline environment of the small intestine. But that's not the whole story.

When food reaches your stomach – be it beef, fish, grains, fruits or vegetables (alone or in combination) – hydrochloric acid is released. The acidic environment of your stomach and its mechanical churning turn food into a partially digested mass called chyme.

Hydrochloric acid also activates a protein-digesting enzyme called pepsin which degrades protein into smaller particles, which must then undergo further digestion in the small intestine.

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When chyme enters the small intestine, the pancreas secretes different enzymes needed to digest protein (protease) into amino acids, carbohydrates (amylase) into glucose and fats (lipase) into fatty acids and glycerol. These small molecules are then absorbed into the bloodstream.

But here's the deal: Your pancreas releases all of these digestive enzymes regardless of what you eat. Whether you eat a steak, a steak with mashed potatoes or simply an apple, your body is primed to digest a mixture of foods. It won't choose between one or the other.

Furthermore, there's no evidence that eating fruit with a meal, or eating brown rice with chicken, for that matter, results in "gut rot." Besides, the harsh acidic conditions of the stomach keep it free of micro-organisms that would putrefy or decompose partly digested food.

Good news. I will still digest my raspberries – and absorb their vitamin C, potassium and phytochemicals – despite the fact that I enjoy them with oats (a starchy food) and kefir (a mix of protein and carbohydrates).

There are reasons, though, why some people don't efficiently absorb nutrients from foods, including lack of stomach acid, prolonged antibiotic use, inflammatory bowel disease and intestinal infections. But these factors are not related to improperly combined foods.

Beneficial food combinations

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There are reasons you should combine certain foods. Eating protein and carbohydrates together, for instance, help keeps you feeling satisfied and energized longer after eating. That's why I advise my clients to include foods rich in both nutrients at breakfast, lunch and midday snacks.

Combining fruit that's high in vitamin C (e.g., strawberries, cantaloupe, citrus) with oatmeal will enhance your body's ability to absorb iron from the cereal.

Adding calcium-rich milk or yogurt to a green smoothie can help bind oxalates from greens such as spinach, an important consideration for people with calcium oxalate kidney stones.

And let's not forget, that some of the healthiest foods on the planet – lentils, kidney beans, black beans and the like – are a combination of protein and carbohydrate.

Leslie Beck, a registered dietitian, is based at the Medisys clinic in Toronto.

Probiotic foods can offer health benefits by promoting the activity of good bacteria in your gut. Leslie Beck explains what to add to your diet so you don't miss out.
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