Food-combining diets say not to mix fruits and vegetables, but your digestive system is really good at its job. It can handle breaking down fruits and vegetables at the same time. There isn't any scientific evidence supporting the theory that eating food groups separately has any beneficial effect.
In fact, mixing fruits and vegetables, as part of an overall healthy diet, can help ensure that you're getting enough vitamins, minerals, antioxidants, phytochemicals and fiber in each meal.
Your digestive system can handle different types of foods at once. The most important thing is to make sure you're eating enough fruits and vegetables to get all the nutrients you need.
Food Combining Philosophy
The basic premise of a food-combining diet is that different categories of foods require different digestive environments. Because of this, proponents of food combining claim that you shouldn't eat certain food categories together because it can inhibit and impair digestion, which leads to rotting of the food in your digestive tract and, eventually, disease.
The principles of food combining state that different types of foods require a different pH and different enzymes to help break them down. The idea of food combining is to eat only the foods that require the same types of environment and enzymes together. For example, according to a food-combining chart, you can eat vegetables with protein, starch or fat, but you should never combine them with fruit.
Supporters of this approach to eating believe that fruit should only be eaten on its own and on an empty stomach because fruit is completely digested in one to two hours, whereas vegetables take closer to two and a half hours. Furthermore, they promote eating food groups separately to help optimize digestion rather than confuse your digestive system. But your digestive system isn't easily confused. In fact, it's efficient and powerful, and it isn't necessary to eat fruits on their own or to avoid eating fruits and vegetables together.
How Digestion Works
It's true that different enzymes break down different types of foods, but your digestive system doesn't pick and choose which enzymes to send out when you eat a meal. The National Institute of Diabetes and Digestive and Kidney Diseases (NIDDK) points out that digestion starts in your mouth, where saliva mixes with food to moisten it and salivary amylase, a digestive enzyme that targets carbohydrates, starts breaking down the starch in both fruits and vegetables. After you swallow, food travels to your stomach where it's mixed with pepsin, an enzyme that breaks down protein, and stomach acid, which is highly acidic.
According to food-combining principles, certain foods need an alkaline environment for proper digestion, while others require an acidic environment; but your stomach acid is always acidic. In fact, it's really acidic, naturally maintaining a pH of about 2.9. There's no way to switch back and forth between an alkaline and acidic digestive environment and, because humans are omnivores and have only one stomach, unlike some herbivore animals, there's no need to. Stomach acid and pepsin mix with food in your stomach, breaking it down even further before it moves on to your small intestine.
Once the partially-digested food reaches the small intestine, it mixes with digestive juices from the intestines, liver and pancreas. The digestive juice, or bile, from the liver contains enzymes called lipase that help break down fat, while the pancreatic juices contain the enzymes trypsin and chymotrypsin to digest proteins; amylase to further break down carbohydrates; and more lipase. Bacteria in your small intestine also help break down the carbohydrates in both fruits and vegetables.
Don't Mix Fruits and Vegetables?
According to the Mayo Clinic, this entire process takes about six to eight hours, not one or two hours, as suggested by food-combining proponents. The process also doesn't identify the carbohydrates and starches in fruits and vegetables differently. In other words, the digestive enzymes that break down carbohydrates don't know the difference between which come from fruit and which come from vegetables.
Your digestive system also sends out all types of enzymes at once into your stomach and small intestine. It doesn't send out specific enzymes that digest only fruits or just vegetables. All of the enzymes and stomach acid do a good job of working together to break down whatever food is eaten.
According to the American Institute for Cancer Research (AICR), food doesn't stay stuck in the digestive tract, rotting. Whatever isn't absorbed in the small intestine moves into the large intestine, where it's either broken down by the good bacteria that live there or eliminated from the body as waste.
Looking at the Science
Aside from breaking down the science of digestion, there hasn't been a lot of research on whether food combining is beneficial in other ways. There was one study, published in the International Journal of Obesity and Related Metabolic Disorders in April 2000, looked at the effects of food combining on weight loss. Researchers put 54 obese participants on one of two diets: a low-calorie food-combining diet or a regular calorie-restricted diet.
Each group's food contained similar amounts of each macronutrient (carbohydrates, protein and fat), but on the food-combining diet, macronutrients were separated from each other at meal times. On the regular low-calorie diet, the macronutrients in meals were mixed. After a period of six weeks, researchers found that weight loss was similar in both groups. Both groups also experienced similar reductions in blood pressure, blood glucose and insulin levels and cholesterol levels.
The group eating mixed meals did have slightly more fat loss, but researchers noted that the difference wasn't really statistically significant. Since this study, there hasn't been much research done on food combining, specifically.
Food-Combining Diet Bottom Line
The Academy of Nutrition and Dietetics agrees that there's no evidence that food combining or eating food groups separately will help with weight loss and that eating a certain combination of foods, like fruits and vegetables, will cause toxic buildup or turn to fat. In fact, eating lots of fruits and vegetables can help promote weight loss and detoxification.
Fruits and vegetables contain many nutrients that act as antioxidants and help neutralize and rid your body of harmful substances called free radicals that can accumulate and may cause chronic disease, like cancer. They're also rich in fiber, which can help keep you full, balance blood sugar and insulin levels and lower bad cholesterol.
The Produce for Better Health Foundation notes that you don't have to worry about separating fruits and vegetables; the most important thing is to make sure you're eating enough of both.
- Mayo Clinic: "Digestion: How Long Does It Take?"
- Michigan Medicine: "Bowel Transit Time"
- International Journal of Obesity and Related Metabolic Disorders: "Similar Weight Loss With Low-Energy Food Combining or Balanced Diets"
- The Ayurvedic Institute: "Incompatible Food Combining"
- Academy of Nutrition and Dietetics: "Staying Away From Fad Diets"
- Produce for Better Health Foundation: "About the Buzz: You Should Eat Fruit on an Empty Stomach?"
- American Institute for Cancer Research: "AICR Health Talk"
- National Institute of Diabetes and Digestive and Kidney Diseases: "Your Digestive System and How it Works"
- Columbia University Irving Medical Center Pancreas Center: "The Pancreas and Its Functions"
- Colorado State University: "Secretion of Bile and the Role of Bile Acids In Digestion"
- PLOS ONE: "The Evolution of Stomach Acidity and Its Relevance to the Human Microbiome"
- Sonnewald Natural Foods: "A Food Combining Chart for Complete & Efficient Digestion"