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Does Food Combining Work? Fact or Fiction

Man in a Kitchen Holding an Apple

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

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

They also believe that proper combinations can relieve these

But is there any truth to these claims?

What Is Food Combining?

Food combining is the term for the idea that certain foods pair
well together, while others do not.

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

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, they’ve become a foundation
for many modern diets.

Generally, food-combining diets assign foods to different

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

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

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

Example Rules of Food Combining

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

  • Only eat fruit on an empty stomach, especially melons.
  • Don’t combine starches and proteins.
  • Don’t combine starches with acidic foods.
  • Don’t combine different types of protein.
  • Only consume dairy products on an empty stomach, especially

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

Two Beliefs Behind Food Combining

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

The first is that, because different 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 digestive and health consequences.

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

The idea is that if two foods require different pH levels, the
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.

It is also believed that the improper combination of foods
leads to negative health consequences such as digestive
distress, the production of toxins and disease.

Bottom Line: Food combining refers to 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 study has examined the principles of food
combining. It tested 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

On both diets, they were only allowed to eat 1,100 calories per

After six weeks, participants in both groups had lost an
average of about 13–18 lbs (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 supposedly
scientific principles of food combining.

Many of the original food-combining diets were developed more
than 100 years ago, when much less was known about human
nutrition and digestion.

But what is now known about basic biochemistry and nutritional
science directly contradicts most of the principles of food

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

On Avoiding Mixed Meals

Meat, Potatoes and Vegetables on a Plate

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 simply not the case. The human body evolved on
a diet of whole foods, which almost always contain some
combination of carbs, protein and fat.

For example, vegetables and grains are typically considered to
be carb-containing foods. But they all also contain several
grams of protein per serving. And meat is considered to be a
protein food, but even lean meat contains some fat.

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. The
enzymes pepsin and lipase are also released, which help start
protein and fat digestion.

Evidence shows that pepsin and lipase are released even if
there is no protein or fat present in your food (2, 3).

Next, food moves into the small intestine. There, the gastric
acid from the stomach is neutralized and the intestine is
flooded with enzymes that work to break down proteins, fats and
carbs (3, 4, 5).

Therefore, there’s no need to worry that your body will have to
choose between digesting protein and fat or starches and

In fact, it’s specifically prepared for this type of

On Food Altering the pH of the Digestive Tract

Pieces of Fruit and Vegetables on Forks

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.

First, a quick refresher on pH. It’s a scale that measures how
acidic or alkaline a solution is. The scale ranges from 0–14,
where 0 is the most acidic, 7 is neutral and 14 is the most

It is true that enzymes need a specific pH range in order 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. Your body has several ways of keeping the pH
of each part of your digestive tract in the correct range.

For example, the 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 is brought back down again (6).

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

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

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The 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 between 5.5 and 7.8 (6, 7).

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

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

If you eat a very acidic or alkaline meal, your body will
simply add more or less digestive juices in order to achieve
the necessary pH level.

On Food Fermenting in the Stomach

Plate with Turkey, Baked Potato and Salad

Lastly, one of the most common claimed effects of improper food
combining is that food ferments or putrefies in the stomach.

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

This simply does not happen.

Fermentation and rotting occur when microorganisms start to
digest your food. But, as mentioned earlier, the stomach
maintains such an acidic pH that your food is essentially
sterilized and almost no bacteria can survive (2).

However, there is one place in your digestive tract where
bacteria thrive and fermentation does occur. This is
in your large intestine, also known as your colon, where
trillions of beneficial bacteria live (8).

The bacteria in your large intestine ferment any undigested
carbs, such as fiber, that were not broken down in your small
intestine. They release gas and beneficial short-chain
fatty acids
as waste products (8).

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 (9, 10).

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

Bottom Line: 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

The principles of food combining diets are not backed by
science, but 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 just a few examples.

Citrus Fruits and Iron

Cut Oranges

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

Heme iron is well absorbed, but the absorption of non-heme iron
is very low — between 1–10%. Luckily, there are several things
you can do to increase the absorption of this kind of iron

Adding vitamin C is one of the most effective things you can

It works in two ways. First, it makes non-heme iron more easily
absorbable. Second, it decreases the ability of phytic
to block iron absorption (12).

This means that combining foods rich in vitamin C (such as
citrus fruits or bell peppers) with plant-based sources
of iron
(such as spinach, beans or 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

Carrots and Fat

Carrot, Celery and Cucumber Sticks in Dip

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. You can get them from veggies like carrots,
tomatoes, red bell peppers, spinach and broccoli.

They have been linked with benefits such as a decreased risk of
certain cancers, heart disease and vision problems (14).

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.

One study examined the absorption of carotenoids with fat-free,
reduced-fat and full-fat dressing. It found that salad had to
be consumed with a fat-containing dressing in order for any
carotenoids to be absorbed (15).

Your best bet to avoid missing out on these important nutrients
is to consume a minimum of 5–6 grams of fat with
carotenoid-containing vegetables (15, 16).

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

Spinach and Dairy Products

Ricotta Cheese and Spinach

Foods such as spinach, chocolate and tea contain oxalate,
an antinutrient that can bind with calcium to form an insoluble
compound (17, 18).

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

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 (17, 18).

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.

But 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

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

Take Home Message

The principles of food combining are not based on science. The
claim that improper food combining is responsible for disease
and toxins in the body is unfounded.

If you feel that the rules of food combining work for you, then
you should certainly continue with it. If your diet isn’t
broken, then there’s no need to fix it.

However, food combining diets may be overwhelming and
unmanageable for a lot of people because of the many
complicated rules they entail.

Plus, there is no evidence that they offer any unique benefits.

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