Food Combining Myths

Is it a bad idea to eat protein and starch at the same meal?

Monica Reinagel, M.S.,L.D./N
4-minute read
Episode #34

Claudia writes:

"I’ve read a lot about food combining, for example, that you should always eat certain types of foods together and avoid certain combinations. Will I lose weight or feel better if I follow these guidelines?"

There is an old but persistent idea that combining certain types of foods at the same meal causes all kinds of bad things to happen to you—everything from indigestion to fatigue to weight gain. There are several variations on this theme but the most common one is that proteins and starches should never be eaten together.

As with so many of the nutrition myths I’ve talked about on this show, this one has a very scientific-sounding explanation, which goes like this: Starches require an alkaline environment for digestion; proteins, on the other hand, require an acidic environment for proper digestion. When you eat these foods at the same time, the digestive system, pulled into two opposite directions, sort of stalls. Food then gets “stuck” in your system, where the carbohydrates ferment and the proteins putrefy, or rot.

When this theory was first put forward at the end of the 19th century, we didn’t completely understand how the human digestive system worked. So, I guess we can cut the originators of this notion a little slack, even though their theory was inherently illogical, for reasons we’ll get to in a moment.

These days, we have a pretty solid understanding of how food gets digested and we can say for sure that this idea is completely false. So, it’s hard for me to understand why these ideas are still floating around. Worse than that, people are still publishing diet books based on them. Let’s see if we can set the record straight.

Working at the Car Wash

Your digestive system is a little like a car wash. When you drive your car through the car wash, a sequence of different chemicals squirts out of a series of nozzles, aimed at various parts of your car. But your whole car goes through the entire car wash together.

Similarly, everything you eat passes through your entire digestive system and the trip is pretty much the same, no matter what kind or combination of food you eat.

First stop, after you chew and swallow your food, is the stomach. Here, food is treated to an acid bath, which serves a couple of purposes. First, the acid kills bacteria and other pathogens that could otherwise make you sick. Secondly, stomach acid begins to break down any proteins and prepare them for later phases of digestion.

Here’s the first chink in the food-combining theory. As Dr. Martin Rehfuss so brilliantly put it, in his 1934 address to the American Medical Association, “A fact that has apparently escaped the proponents of the carbohydrate-alkaline theory is that no carbohydrates are ingested which are not followed by a direct acid response on the part of the stomach.” I wish I had known Dr. Rehfuss. He sounds like my kind of guy.

Next stop in the digestive car wash is the small intestine. Here the stomach acid is neutralized by pancreatic juices and this allows a variety of enzymes to go to work. (Most enzymes don’t work too well in acidic environments.) There are enzymes that digest protein, enzymes that digest carbohydrates, and enzymes that digest fat. But the full array of enzymes is produced every time, no matter what you eat.

Not only is your digestive system capable of digesting a combination of protein and carbohydrates, but it appears as if this is the default setting. And if you think for just a moment, you’ll realize how illogical it is to think that the body might have been designed to digest proteins separately from carbohydrates.

Most Starches Contain Protein, and Vice Versa

We could spend the rest of the day arguing about whether humans are meant to consume grains or animal proteins but I think we’d all have to agree that humans were definitely meant to consume breast milk as infants. Breast milk contains both protein and carbohydrates. And as Glenn Cardwell so colorfully put it, in an article for The Skeptic, “No woman has been born with one breast labeled ‘protein’ and the other ‘carbohydrate.’” Quite a visual, isn’t it?

In fact, most foods that we would identify as starches contain protein. About 14% of the calories in spaghetti, for example, are from protein. Rice and potatoes contain about 8% of calories from protein and wheat bread contains about 16% of calories from protein.

On the flip side, beans and legumes, foods which supply much of the world’s protein needs, contain roughly as much carbohydrate as they do protein. Proponents of food combining recoil in horror at the idea of eating steak and potato at the same meal but would approve of a nice bowl of black bean soup. And yet the two meals contain roughly the same proportion of protein and carbohydrate.

Now, despite everything I’ve just said, a lot of people swear that following these guidelines makes them feel better or helps them lose weight. And you know what? It just might. And here’s why:

An Unadvertised Benefit

Food-combining rules have an unadvertised benefit: You often end up eating less when you are following them. Typical restaurant meals, for example, include protein, starch, and vegetables. If you are following the rules, some portion of that meal will remain on your plate. And even when you are cooking for yourself, research shows that when a meal contains fewer different things, you tend to eat fewer calories. (If that sounds unlikely, stop for a moment to recall how much you ate the last time you were faced with a buffet.)

Not overfilling your stomach can definitely improve digestion, reduce fatigue, and enhance weight loss. You could probably get the same results by simply cutting back on portion sizes. But, if following these rules works for you, go for it. Just know that there is no physiological or biochemical reason to avoid combining protein and starch.

In fact, there is at least one reason you might want to go out of your way to combine protein with starch. Eating protein with carbohydrates tends to smooth out the rise in blood sugar that happens when you eat carbs by themselves. And that sounds like a good topic for a future show.


This is Monica Reinagel, the Nutrition Diva, with your quick and dirty tips for eating well and feeling fabulous.

Have a great day and eat something good for me!


Food Combining Myths Debunked (Glenn Cardwell for The Skeptic)

Variety in a Meal Enhances Food Intake (Barbara Rolls, et al., in Physiology and Behavior)

Effects of Protein and Fat on Glycemic Response (Elham Moghaddam, et al. in Journal of Nutrition)