We are often asked, “Is it safe to mix fruits and vegetables in my smoothie?  What about ‘food combining’?”

The most relevant point in considering whole food blending is that when using a high-speed blender, you are "homogenizing" the foods, which makes it one drink (just like eating a food that contains a spectrum of macronutrients: fat, protein, carbohydrate, etc.), so your body digests as such, not as if the foods were separate foods.  Secondly, the blender pre-digests the food, breaking down the cell walls so the body doesn't work as hard in the digestive phase of metabolism.  

Still, I was compelled to look further into this food combining theory to find out just what the real deal was…

One very important clarification to start with is that greens, including kale, spinach, romaine lettuce, etc., are NOT the same as starchy vegetables, which are what most warnings against combining fruits and vegetables are based on.  They are plants, just as the green tops of carrots are not the same as the carrots themselves.  There are a variety of categories of fruits and vegetables, including starchy, greens, sweet fruits, sour fruits, and so on.  Lumping them together is a common mistake. Greens are perfectly fine to mix in smoothies.  Actually, greens are the only foods that help digest other foods through stimulating the release of digestive enzymes.

Some proponents of food combining include carrots (and beets) as starchy foods to avoid mixing, some say that carrots are an exception.  The biggest thing (because EVERYONE has different reactions, and some people are just fine mixing anything and everything, while others experience better feelings and results by adhering to different rules) is how is YOUR body reacting? Are you gassy, bloated, and constipated?  If so, first thing to do is slow down and "chew" your smoothie, which helps stimulate the release of the enzymes in your small intestines. If you still experience digestive disturbances, then try reducing ingredients.  

Surprisingly, there is little direct research on food combining ideas.  Many of the rules say no dairy with fruit, no carbs with meat, no vegetables with meat...  do you divide these foods? How many people do you know are doing that? And in direct contrast to these rules, we know that consuming salad, for example, requires a fat such as oil in order to really absorb the nutrients, such as carotenoids. 

The only reasonable theory behind not combining fruits and vegetables is that fiber and oxalates can bind to minerals like calcium, magnesium and potassium and prevent their absorption, but that does not require food combining as high-oxalate vegetables by themselves would do that without eating anything else.

The original and main principle behind food combining was/is based around the pH levels required for digestion and it's effects on nutrient absorption and digestion time.  The 4 common rules cited are:

  • "Always eat fruit alone and at least 20 minutes before anything."
  • "Eat starches alone or with cooked non-starchy vegetables."
  • "Eat meat, dairy, fish, eggs and other high protein foods alone or with cooked non-starchy vegetables"
  • "Eat nuts, seeds, dried fruit with raw vegetables."


A deeper look reveals that these rules are not supported by any evidence and most are myths.

First we will address that carbohydrates digest better in an alkaline environment. This is true as amylase enzymes only occur in the mouth and then intestines.  Here is the biochemistry: The stomach is always acidic when eating any food as the stomach acids are released every time you eat, no exceptions.  When what you have eaten enters the stomach, it is formed into a substance called chyme, which is then released into the small intestine and acted upon all together.  The pancreas then releases it's own digestive enzymes along with bicarbonate to neutralize the stomach acid and create alkaline environment for carbohydrate digestion.  However, this process is triggered proportionally to the level of the pH (acidity) of the contents entering the small intestines.  Eating protein with carbs or fats, then, may actually increase digestive capacity and help digestion, which is exactly the opposite of this theory.

Secondly, your body makes the enzymes that release into the small intestines: lipase, amylase and trypsin, to work on different components of the food: carbs, fat, protein.  So based on the very processes of the body, we can see it basically knows that it is going to get a mix of nutrients.  

We now know that when you eat, everything passes through the digestive tract the same. The enzymes produced in the small intestines are produced EVERY TIME...regardless of what you eat... and what is needed at that time gets used.  In fact, based on our modern understanding of the biological processes, we find that digesting protein and carbs together is the default setting of the body...which would be a no-no based on these common food
combining rules.

Many foods contain multiple macronutrients all in themselves, so obviously the body can handle processing more than one at a time.  Take the white potato (which we don't eat, by the way, because it is SO starchy)...8 ounces of a baked white potato contains 4.76g of protein and 1% of your RDA of fat.  Yet it is considered a starchy carbohydrate.

The theories of food combining were originally introduced at the end of the 19th century.  While our understanding biologically has grown, some myths still persist.  Many of the "problems" brought up in regard to food combining are indigestion, weight gain and fatigue.  It's not hard to see why many people report improvements on these conditions when following these guidelines.  They are eating cleaner and less.  Naturally, less food is consumed at one time if you are just eating your vegetables alone, waiting, eating the next food alone, and so on.  When you are not overfilling, that naturally improves digestion, reduces fatigue and enhances weight loss.

The biggest telltale sign is how things react in your body.  It would be like your neighbor saying they get really bad gas when they eat garlic, so therefore garlic cannot be properly digested, causes gas, and no one should eat it.  We frequently hear and repeat without much personal verification, and our instant access to perceived facts on the internet and social media tend to propagate the information with little understanding of actual journaled research to support the claims.  

As always, do not rely on someone else to care for your health.  Educate and empower yourself, and take charge of your own health!