Food combining is a philosophy of eating that has ancient roots but has become extremely popular in recent years.

Proponents of food-combining diets believe that improper food combinations can lead to disease, toxin buildup, and digestive issues.

They also believe that proper combinations can actually help relieve these problems.

But is there any truth to these claims? This article will take a closer look at the research to determine whether food combining is effective.

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Nadine Greeff/Stocksy United

What is food combining?

Food combining is a concept based on the idea that certain foods pair well, while others do not.

The belief is that combining foods improperly — for example, eating steak with potatoes — can lead to negative effects on health and digestion.

Food-combining principles first appeared in the Ayurvedic medicine of ancient India, but they became more widely popularized in the mid-1800s under the term “trophology,” or “the science of food combining.”

The principles of food combining were revived in the early 1900s by the Hay diet. Since then, food combining has become a popular practice supported by some in the health and wellness world.

Generally, food-combining diets assign foods to different groups.

These are usually broken down into carbs and starches, fruits (including sweet fruits, acidic fruits, and melons), vegetables, proteins, and fats.

Alternatively, some plans classify foods as acidic, alkaline, or neutral.

Food-combining diets specify how you should combine these groups in a meal.

Common rules of food combining

The laws of food combining can vary somewhat depending on the source, but the most common rules are:

  • Eat fruit only on an empty stomach, especially melons.
  • Avoid combining starches and proteins.
  • Avoid combining starches with acidic foods.
  • Avoid combining different types of protein.
  • Consume dairy products only on an empty stomach, especially milk.

Other rules say that protein should not be mixed with fat, sugar should only be eaten alone, and fruits and vegetables should be eaten separately.

Beliefs behind food combining

The rules of food combining are mostly based on two beliefs.

The first is that, because foods are digested at different speeds, combining a fast-digesting food with a slow-digesting food causes a “traffic jam” in your digestive tract, leading to negative effects on health and digestion.

The second belief is that different foods require different enzymes to be broken down and that these enzymes work at varying pH levels — levels of acidity — in your gut.

The idea is that if two foods require different pH levels, your body cannot properly digest both at the same time.

Proponents of food-combining diets believe that these principles are essential to proper health and digestion.

They also believe that improper combining of foods causes toxins to build up and leads to negative health consequences such as digestive distress and disease.

Summary

Food combining is a way of eating in which certain types of foods are not eaten together. Proponents of food-combining diets believe improper combinations lead to disease and digestive distress.

What does the evidence say?

So far, only one 2000 study has examined the principles of food combining. It looked at whether a diet based on food combining had an effect on weight loss.

Participants were split into two groups and given either a balanced diet or a diet based on the principles of food combining. On both diets, they were allowed to eat only 1,100 calories per day.

After 6 weeks, participants in both groups had lost an average of 13–18 pounds (6–8 kg), but the food-combining diet offered no benefit over the balanced diet (1).

In fact, there is no evidence to support most of the principles of food combining. What’s more, many of the original food-combining diets were developed more than 100 years ago, when much less was known about nutrition and digestion.

What we now know about basic biochemistry and nutritional science directly contradicts most of the principles of food combining.

Here’s a closer look at the science behind the claims.

On avoiding mixed meals

The term “mixed meals” refers to meals that contain a combination of fat, carbs, and protein.

The rules of food combining are largely based on the idea that the body is not equipped to digest mixed meals.

However, this is not the case, as the human body evolved on a diet of whole foods, which almost always contain some combination of carbs, protein, and fat (2).

For example, vegetables and grains are typically considered carb-containing foods, but they all also contain several grams of protein per serving. Additionally, although meat is considered a protein food, even lean meat contains some fat (3, 4).

Therefore, because many foods contain a combination of carbs, fat, and protein, your digestive tract is always prepared to digest a mixed meal.

When food enters your stomach, gastric acid is released along with the enzymes pepsin and lipase, which help start digestion of protein and fat (5).

Research shows that pepsin and lipase are released even if your food contains no protein or fat (6, 7).

Next, food moves into your small intestine. There, the gastric acid from your stomach is neutralized and your intestine is flooded with enzymes that work to break down proteins, fats, and carbs (7, 8).

For this reason, there’s no need to worry that your body will have to choose between digesting protein and fat or starches and proteins. In fact, it’s specifically prepared for this type of multitasking.

On food altering the pH of the digestive tract

Another theory behind food combining is that eating the wrong foods together can hinder digestion by creating the wrong pH for certain enzymes to function.

The pH scale measures how acidic or alkaline a solution is. It ranges from 0–14, where 0 is the most acidic, 7 is neutral, and 14 is the most alkaline (9).

It is true that enzymes need a specific pH range to function properly and that not all enzymes in the digestive tract require the same pH.

However, eating foods that are more alkaline or acidic does not significantly change the pH of your digestive tract, and your body has several ways of keeping the pH of each part of your digestive tract within the correct range (10).

For example, your stomach is usually very acidic, with a low pH of 1–2.5, but when you eat a meal it may initially rise as high as 5. However, more gastric acid is quickly released until the pH comes back down (11).

Maintaining this low pH is important because it helps start the digestion of proteins and activates the enzymes produced in your stomach. It also helps kill any bacteria in food.

In fact, the pH inside your stomach is so acidic that the only reason your stomach lining isn’t destroyed is that it’s protected by a layer of mucus (12).

Your small intestine, on the other hand, is not equipped to handle such an acidic pH.

Your small intestine adds bicarbonate to the mix as soon as the contents of your stomach enter it. Bicarbonate is your body’s natural buffering system. It’s very alkaline, so it neutralizes the gastric acid, keeping the pH around 6–7 (5).

This is the pH at which the enzymes in your small intestine function best.

In this way, the different levels of acidity in your digestive tract are well controlled by your body’s own sensors.

If you eat a very acidic or alkaline meal, your body will add more or less digestive juices as needed to achieve the necessary pH level (5).

On food fermenting in the stomach

One of the most common supposed effects of improper food combining is that food ferments or putrefies in your stomach.

Supposedly, when a fast-digesting food is combined with a slow-digesting food, the fast-digesting food stays in your stomach so long that it begins to ferment.

However, this does not happen.

Fermentation and rotting occur when microorganisms start to digest your food. But, as mentioned earlier, your stomach maintains such an acidic pH that almost no bacteria can survive (6).

There is one place in your digestive tract where bacteria thrive and fermentation does occur. This is your large intestine, also known as your colon, where trillions of beneficial bacteria live (13).

The bacteria in your large intestine ferment any undigested carbs, such as fiber, and release gas and beneficial short-chain fatty acids as waste products (14).

In this case, fermentation is actually a good thing. The fatty acids the bacteria produce have been linked to health benefits such as reduced inflammation, improved blood sugar control, and a lower risk of colon cancer (15, 16).

This also means that the gas you experience after a meal is not necessarily a bad thing but instead can be a sign that your friendly bacteria are well-fed.

Summary

There is no evidence that the practice of food combining offers any benefits. In fact, modern science directly contradicts many of its principles.

Evidence-based examples of food combining

Although the principles of food combining diets are not backed by science, that doesn’t mean that the way you combine foods is always irrelevant.

For instance, there are many evidence-based food combinations that can significantly improve or reduce the digestion and absorption of certain foods.

Here are a few examples.

Citrus fruits and iron

Iron comes in two forms in the diet: heme iron, which comes from meat, and non-heme iron, which comes from plant sources (17).

Heme iron is well absorbed, but your body’s absorption rate for non-heme iron is very low — from 1–10%. Luckily, there are several things you can do to increase your absorption of this kind of iron (18).

Adding vitamin C is one of the most effective ways to increase iron absorption.

In addition to making non-heme iron more easily absorbable, vitamin C decreases the ability of phytic acid to block iron absorption (19).

This means combining foods rich in vitamin C (such as citrus fruits and bell peppers) with plant-based sources of iron (such as spinach, beans, and fortified cereals) is an excellent choice.

Unfortunately, studies have not shown that this combination actually increases iron levels in the body. However, this could simply be because the studies to date have been too small (20).

Carrots and fat

Certain nutrients, such as fat-soluble vitamins and carotenoids, need fat in order to be absorbed by the body.

Carotenoids are compounds found in red, orange, and dark green vegetables, including carrots, tomatoes, red bell peppers, spinach, and broccoli (21).

Studies show that carotenoid-rich diets may reduce the risk of some health conditions such as certain cancers, heart disease, and vision problems (22).

However, research has shown that if you consume these vegetables without any fat — eating plain carrot sticks or salad with fat-free dressing, for instance — you may be missing out on the benefits.

In fact, one small study found that consuming vegetables with salad dressings that contain higher levels of fat was associated with increased absorption of carotenoids (23).

Your best bet to avoid missing out on these important nutrients is to pair carotenoid-containing vegetables with heart-healthy fats, like nuts, seeds, olive oil, or avocados (24).

Try adding some cheese or olive oil to your salad or topping your steamed broccoli with a little bit of butter.

Spinach and dairy products

Foods such as spinach, chocolate, and tea contain oxalate, an antinutrient that can bind with calcium to form an insoluble compound (25).

This can be good or bad for you, depending on the circumstances.

For people who are prone to certain types of kidney stones, consuming calcium sources such as dairy products with oxalate-containing foods can actually decrease the risk of developing kidney stones (26).

On the other hand, combining oxalates and calcium decreases the absorption of calcium. For most people, this is no problem in the context of a balanced diet (27).

However, for people who don’t eat much calcium in the first place or who eat a diet very high in oxalates, this interaction might cause a problem.

If you are concerned about getting enough calcium from your diet, avoid combining dairy products and other calcium-rich foods with foods that are high in oxalates.

Foods that are high in oxalates include spinach, nuts, chocolate, tea, beets, rhubarb, and strawberries, among others (25).

Summary

The principles of most food-combining diets are not evidence-based. However, a few food combinations have been scientifically shown to affect the digestion and absorption of nutrients.

The bottom line

Most of the principles of food combining are not based on science, and there is no evidence to support the idea that improper food combining contributes to disease or toxins in the body.

Furthermore, because there are so many rules and regulations, some people may find that food-combining diets can be complicated and difficult to follow.

However, it is fine to incorporate the principles of food combining into a healthy, well-rounded diet if you find that it works for you.