Supporters say that not mixing some foods helps digestion and prevents weight gain, so we took it to a pro for answers.

By Cynthia Sass, MPH, RD
November 30, 2020
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Clients often ask me about food combining, and there are three potential strategies they're inquiring about that use this terminology. Only one has merit scientifically. But, I think it's helpful to understand the reasoning behind each food combining approach, and why simply focusing on eating a varied, balanced diet with plenty of whole foods is the best tactic to maximize your nutritional status and health. Here's what to know.

You don't need to avoid combining certain foods 

One method of food combining focuses on not mixing certain macronutrients (protein, carbs, and fat), not eating certain food groups together (such as starches and protein, or fat and protein), and only eating some foods by themselves, like fruit. The theory is that eating certain foods together interferes with digestion—because of the differing enzymes needed or the varying pH level or rate of digestion of these foods. Proponents of this type of food combining believe that "competition" in the gut causes food to "rot" in the body, which leads to the production of toxins, and triggers digestive distress and health problems.

The truth is that these food combining rules don't make much sense for several reasons. First, your body does a very good job of releasing the enzymes needed to digest a meal, regardless of what you have consumed. In other words, your body supplies what is needed to accomplish the job of breaking down your food and absorbing the nutrients from your GI tract into your bloodstream.

Many supporters of food combining claim that not following it leads to weight gain. However, if food isn't digested properly, the result is malabsorption, which leads to loose stools or diarrhea, and weight loss, not weight gain. The vast majority of the population does not practice food combining, and we do not have an epidemic of malabsorption and weight loss.

Also, many single foods contain a combination of macros, such as nuts, which provide fat and protein, and lentils, which provide carbs and protein. If the principles of food combining held true, your body would have a difficult time digesting these foods, even when eaten alone.

In addition, in the five areas of the world known as The Blue Zones—where people live the longest, healthiest lives—inhabitants do not practice food combining. It's quite the opposite in these regions, where a high percentage of citizens live to be 90 and above, but the rates of obesity and other diseases are quite low. For example, in Ikaria, Greece, lunch may be salad with beans and potatoes; in Nicoya, Costa Rica, is can mean beans, rice, and squash. Neither meal adheres to food combining theory, which further diminishes its validity.

Finally, certain food pairs that directly defy the rules of food combining can actually help improve nutrient absorption (more on this below). And, while there is only one published study that has specifically looked at food combining, researchers found no significant difference in the amount of weight loss or body composition changes between subjects who followed food combining guidelines and those who simply ate a balanced diet over a six-week period. There were also no differences in fasting blood sugar or insulin levels, or in total cholesterol and blood fat concentrations.

Vegans shouldn't worry about eating certain foods together

Another food combining question I'm often asked is if vegans need to eat certain foods together, like beans and rice, in order to create "complete" proteins. The answer is no—if you eat a varied diet and consume enough total protein and calories. An older theory was that in order to utilize plant protein efficiently, you must eat complimentary proteins simultaneously. For example, rice and beans were thought to be complimentary because the key amino acids (the building blocks of protein) that are low in beans are high in rice, and vice versa.

Fortunately, your liver does a great job of storing various essential amino acids over the course of a day for later use. These amino acids then come together to effectively build or repair protein tissues in the body. Rather than eating specific combos, the best approach is to consume enough of a wide variety of plant foods daily, in order to take in a broad spectrum of both amino acids and other nutrients.

But some food combos do make sense

The final strategy that some people refer to as food combining has to do with eating foods in duos that boost the absorption of a certain nutrient or nutrients. For example, only 2% to 20% of the iron found in plant foods, called non-heme iron, makes its way from your digestive tract into your blood. But consuming a source of vitamin C increases non-heme iron absorption by as much as six times.

For this reason, food combinations that supply both nutrients are encouraged, especially for vegans, such as broccoli (iron) with tomatoes (vitamin C), black beans (iron) with red bell pepper (vitamin C), kale (iron) with oranges (vitamin C), and dark chocolate (iron) with strawberries (vitamin C).

Another smart combo is fat with produce. Fat has been shown to significantly increase the absorption of fat-soluble vitamins and antioxidants in fruits and veggies. In one study, adults absorbed significantly more beta carotene from both tomato sauce and carrots when these foods were combined with avocado, a healthy fat source.

Other research found that essentially no carotenoid antioxidants were absorbed from salads dressed with fat-free dressing, compared to a high level of absorption when full-fat dressing was used.

For this reason, it's a very good idea to not follow one of the key food combining principles above that calls for eating fruit by itself. Pairing fruit with healthy fats like nuts, seeds, or nut/seed butters, olives, or avocado will help you get more nutrition. As a bonus, it will also better regulate your blood sugar and insulin levels, which can spike when fruit is consumed solo.

Bottom line about food combining

Apart from examples where pairing certain foods together can boost nutrient absorption, don't focus on rules about foods that should and shouldn't be eaten together. The best way to ensure that you take in a broad spectrum of nutrients is to choose whole foods over highly processed versions, consume a variety of foods, and tune into hunger, fullness, and energy cues to decide when and how much to eat. Establishing a consistent eating routine can help, such as eating three to five meals a day around the same times.

Cynthia Sass, MPH, RD, is Health's contributing nutrition editor, a New York Times best-selling author, and a private practice performance nutritionist who has consulted for five professional sports teams.

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