What’s the buzz?
That you should avoid eating certain foods together or risk digestive distress and damaging your weight-loss efforts.
What does the science say?
One popular diet trend — known as “food combining” — tells us that to reach optimal digestive health and shed a few pounds, you should avoid eating certain foods together. There are five main rules: only eat fruit on an empty stomach, don’t combine starch and protein, don’t combine starch with acidic food, don’t combine different proteins, and only consume dairy on an empty stomach. You can eat non-starchy vegetables with most foods (except fruit). So yes, that means that this diet says you’ll have to ditch your avocado toast, green protein smoothies, and almost anything you might consider to be a balanced meal.
The theory behind these recommendations is that protein, carbs, and fat are broken down by unique enzymes that require different pH levels to function. Proponents of the diet suggest that by combining protein and carbs, for example, those nutrients aren’t fully digested and food gets “stuck” in your digestive tract because the correct enzymes either aren’t released or the pH of your digestive tract changes due to the food.
While in the simplest of terms, it is true that some enzymes require more acidic environments than others, food is digested and metabolized throughout the entire digestive tract, from mouth to large intestine. Regardless of whether you’re eating foods together or separately, every food passes through the entire digestive tract, which includes environments that are very acidic (stomach) and less acidic to neutral (mouth and small intestine) environments.
Our bodies tightly regulate the pH of the entire digestive tract. Each enzyme involved in the digestive process gets secreted in the environment it functions best in — regardless of what type of food you ate. Enzymes that break down carbs, protein, and fat are all secreted in the small intestine, and evidence shows that pepsin and lipase, two enzymes that break down protein and fat are secreted even when you eat foods that contain only carbohydrate.
Anatomy and physiology aside, most foods contain a mix of protein, carbohydrates, and fat, so it would be impossible to completely separate these nutrients in your diet.
As for the research on this diet, it’s pretty scarce. One small study on this topic found there was no difference in weight loss between a standard diet and a food combining diet when calories were kept consistent. In fact, it’s often recommended that you pair carbohydrates with protein and fat to slow digestion and improve satiety, which can help with weight management. Fat-soluble vitamins and some antioxidants that are found in fruits and both starchy and non-starchy vegetables are better absorbed when consumed with foods that contain fat. Additionally, some research has shown that consuming foods high in oxalate (a compound known to increase risk of kidney stones) with calcium-rich foods like dairy products may reduce risk of kidney stones.
What’s the takeaway?
Food combining is not only complicated and hard to follow, there is no science to back up the theory that it will improve digestion or weight loss efforts. Our bodies have very intricate, well-regulated systems to break down nutrients, and in some cases eating certain foods together may actually be more beneficial than eating them alone.