Without fail, every time I post a green smoothie recipe that includes a carrot or a stalk of celery or piece of cucumber, I’ll get comments from concerned people who’ve heard that one should never mix fruits and vegetables. It’s “bad food combining”, they say.
Blending acid fruits like pineapple or citrus with sweet fruits like bananas are supposedly no-nos. Watermelon smoothies shouldn’t even be a thing because watermelon is supposed to be eaten by itself.
But is this really so? Does making a green smoothie break any rules? Will improperly combining foods cause health and digestion problems?
The answer is no. There is absolutely no scientific basis for adopting rules about food combining.
In fact, the food combining hypothesis was thoroughly debunked almost 80 years ago, there is absolutely zero scientific evidence to support it, and no credible scientists or doctors support food combining today.
What Is Food Combining?
Food combining is a central tenet of the Natural Hygiene philosophy, which was founded by Sylvester Graham in the 1830s and was brought into the 20th century by Herbert M. Shelton. Elements of Natural Hygiene are particularly popular in the modern raw food movement, and “proper food combining” is often dictated on raw food message boards and websites.
The food combining hypothesis states that certain food combinations should never be consumed since such combinations will disrupt the body’s balance, cause digestion problems, and lead to poor health and “toxic buildup”. The idea is that certain foods digest using different enzymes, and improper food combining confuses the body, thereby producing health-damaging side effects from digestion.
Food combining “no-no’s” include mixing protein with fat, or protein with carbohydrate. Fruit should always be eaten separately, and certain types of fruit should not be mixed, for example, “acid fruits” like oranges with “sweet fruits” like bananas. Melons should always be eaten on their own.
Many of my green smoothie recipes are at odds with food combining since I routinely blend pineapple with banana (gasp!) and I also commit the unforgivable sin of blending melons with just about every fruit and vegetable you can think of. Yes, I’m an evil melon blender!
Do I care that I break just about every single food combining rule every day? No! I don’t care because there is absolutely no reason why I should. The food combining hypothesis is not grounded in science, and it is not supported by personal experience or observation.
Why Is The Food Combining Hypothesis Unscientific?
The food combining hypothesis is not scientific, that is, it does not hold up to the rigors of the scientific process. It is pseudoscience, with a tidal wave of modern science punching holes in the idea.
Food combining is not supported by credible scientists and doctors (it is not even supported by many natural health experts). And when I say “credible”, I’m referring to scientists and doctors who’ve studied at accredited schools, and who abide by the scientific process, and who utilize the peer-review process to separate truth from wishful thinking and incorrect assumptions spun as “common sense” on the Internet.
Food combining doesn’t stand up to the rigors of scientific scrutiny and what we know of human digestion has advanced greatly in the 170 years since food combining and Natural Hygiene came onto the scene.
In short, there is no credible scientific evidence that eating a meal with protein and carbohydrates together will cause any problems with digestions, enzyme imbalance, or produce toxic aftereffects. There is no evidence that fruits and vegetables cannot be digested together, or require different enzymes, and that mixing the two will cause health problems.
The mixing of fruits with vegetables, or protein with carbohydrate, has not been scientifically established as a cause or contributing factor in vitamin and mineral malabsorption.
An often cited criticism of food combining is that foods themselves have differing amounts of macronutrients that supposedly should not be combined. For example, beans contain a combination of carbohydrates and protein. Meat and eggs contain a combination of protein and fat. All fruits and vegetables contain varying ratios of carbohydrate, protein and fat.
What Happens When You Combine Watermelon With Other Fruits/Vegetables?
Watermelon is about 92% water and 6% sugar, so the reasoning is that since it digests so quickly, it should be eaten on its own. If you were to eat a slower digesting fruit, they say, with watermelon, you’d cause the watermelon to become slowed down in your digestive system where it will ferment.
However, this is not what happens when you combine watermelon with other fruits.
One cup of watermelon is 89% carbs, 7% protein and 4% fat with 9.2 grams of sugar and .6 grams of fiber. If you toss one cup of sliced apple into your blender with the watermelon, you won’t be creating a digestion bomb.
All you are doing is creating a food with a slightly different nutritional makeup – 92% carbohydrate, 4% protein, 4% fat with 20.7 grams of sugar and 3.2 grams of fiber. That’s a pretty average macro-nutrient ratio that most fruits have.
Your stomach and digestive system doesn’t know the difference between a watermelon and an apple, or a combination of the two, or a different fruit which has a similar macro-nutrient ratio.
Toss in a cup of fresh baby spinach and all you are doing is creating a “new” food that has a different ratio of carbs/protein/fat. Your body will digest it in the time it needs to digest it. Your body won’t select the fastest digesting fruit, and let everything else “rot” in your gut.
Personal Experience With Food Combining
From personal experience, I have never once experienced any side effects of blending oranges, plums or pineapples (acid fruits) with bananas, grapes or papayas (sweet fruits). I’ve never once experienced side effects from blending greens with fruits, or fruits with vegetables such as zucchini, cucumber, carrot, broccoli, celery, bell pepper, beet and tomato.
I have never personally seen a single instance where any of the above combinations caused any physical or digestive problems in a person with a healthy, normally-functioning digestive system.
But Why Do I Not Feel Right After Combining Certain Fruits and Vegetables?
Despite the fact that there is zero science that supports food combining, and a significant lack of credible health professionals who support the hypothesis, there are adherents who claim that they had trouble with digestion and chronic illness until they finally got on the food combining bandwagon. They cite their experiences as proof that food combining works.
So does that mean that food combining works for some and not others? Does it mean that there is anything at all to the 170-year old notion of food combining?
Not really. There can be a lot of factors that could cause digestion issues, or chronic feelings of poor health, that might be otherwise blamed on improper food combining. The four most common include:
- Allergies and intolerance to certain fruits (but not combinations of different fruits). Some people have bad reactions to certain fruits, but it’s not necessarily because those fruits were mixed with the wrong types.
- Lack of thorough chewing, particularly in the case of a green salad topped with fresh fruit. In this instance, the issue is the larger pieces of food being more difficult to digest (plant cellulose in leafy greens) rather than that greens and fruit are being mixed.
- Underlying health problems that affect digestion and/or nutrient absorption that have nothing at all to do with combinations of certain foods, but that might be exacerbated by certain combinations in certain individuals.
- Digestive “issues” like gas and bloating that occur when people make a sudden dietary change by eating more fruits and vegetables. This has more to do with a sudden increase of fiber and the body adjusting to different foods and nothing at all to do with food combining, and it goes away in a few days.
The above issues should be ruled out before a 170-year old, thoroughly debunked dietary philosophy is given credence, despite its lack of scientific support.
If It Feels Good, Drink It!
The rigid rules of food combining makes eating complicated, isn’t necessary, and doesn’t serve me. My approach to diet and green smoothies is that if it feels (and tastes) good, I’ll keep drinking it!
That includes my citrus-banana smoothies, and my plum-papaya creations, and blending every fruit I can get my hands on with every vegetable I’m brave enough to toss into my blender pitcher. And watermelon smoothies! Ignore the rules and enjoy your green smoothies instead!
Hi! I'm Tracy - green smoothie addict since 2008 and creator of BLEND: A 10-Day Green Smoothie Cleanse.
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