When I first heard about food combining I thought it was simply about balancing all three macronutrients (fat, protein, carbohydrates) at a meal. Nope - in fact, it's actually the opposite! Food combining is a diet with Ayurvedic roots, and there are quite a few rules. Food combining seems to be gaining popularity again, so I think it's time to dive into the question, "what is food combining?" and see what the research says.
As always, I aim to provide unbiased information. I look at the science of nutrition and the human body, along with available research and evidence. As a registered dietitian, my goal isn't to tell you what to do, but to present available science-based information to help you make informed choices with your personal health and nutrition.
What is food combining?
Food combining is a dietary approach that promotes eating foods in specific combinations thought to improve health, digestion, and weight loss.
The Claims of Food Combining
According to the theories behind it, food combining leads to digestion that is better, faster, more efficient, and just generally improved. In theory, this also helps reduce toxins and disease. Food combining is also said to possibly help with weight loss and many food combining enthusiasts have personal weight loss testimonies to share.
Food Combining Rules
There are a lot of food combining rules and guidelines, although there can be some variance depending on the source. Some rules include:
- Fruit must be eaten on an empty stomach - especially melons.
- Don't combine starch and protein.
- Dairy products must also be consumed on an empty stomach - especially milk.
- Don't combine protein and fat.
- Different types of protein shouldn't be combined.
- Sugar should only be eaten on an empty stomach.
- Don't combine starches and acidic foods.
The Origin and Theory Behind Food Combining
There seem to be two main philosophies behind food combining. The first dates back to ancient Ayurvedic practices. The second is based on foods being acidic, alkaline, or neutral, which requires different digestive pH levels and individual gastric transit times for digestion.
Ayurvedic Food Combining
Food combining has some roots in Ayurvedic medicine, a medical system with natural approaches to physical and mental health. Ayurveda medicine has ancient roots but is still in use today in different applications.
Ayurvedic food combining is theorized to help promote faster, more efficient digestion by focusing on consuming beneficial combinations and avoiding food combos that may slow and harm digestion.
One analogy often used is that your stomach is like a one way street. Different foods digest at different rates, so if you (for example) eat meat, a slower digesting food, then eat fruit, a faster digesting food, the fruit will take longer to digest, which can lead to rot and toxins that will build up in the system.
Food Combining and pH Balance
Another theory behind food combining centers around the pH levels (or acidity vs alkalinity) of foods. This stems from "the Hay diet" created by Dr. William Howard Hay in the 1920s. This philosophy says that the different enzymes required to break down different types of food work at different pH levels in your body. So, in theory, if you're consuming two foods requiring two different pH levels, the body won't be able to fully digest either food at the same time. This digestive incompatibility leads to impaired nutrient absorption and decreased gastric motility. Decreased motility means the food is just "sitting" in the gut longer, creating gas, bloat, toxins, and disease.
The primary foods that seem to be problematic with each other according to this theory seem to be protein-rich foods and carbohydrate-rich foods. But essentially, the goal is to not consume more than one macronutrient at once.
The Science Behind Food Combining
There is extremely limited science behind food combining. There is also a shockingly almost non-existent level of research on food combining.
I was only able to find one research article actually using food combining principles in a study. The study compared an experimental group and a control group, both with very similar calories and macronutrient breakdown, but with the foods in the experimental group consumed in combinations honoring food combining principles. The findings showed zero differences in weight loss results from the food combining diet and the balanced diet.
Absence of Evidence vs. Evidence Against
I want to take a moment to share an important reminder: the absence of evidence does not mean evidence against. But in the case of food combining, a diet rooted in such ancient medicine (aka not a trend from the past month) and that has been cycling in trendiness for decades, it should be a red flag that there is only one study available.
So why? Why, for a diet that's been around for so long, is there only one research study? And why is there no research into the food combining claims on digestion and the one article was only about weight loss?
Well, it's because what we know about science and the human body now compared to thousands of years ago invalidates many principles of food combining. Remember learning about the Medieval ages in school and hearing how doctors practiced crazy things like bloodletting in the name of medical treatment? And how we'd kind of shake our heads because we know better now? Sure, small amounts of bloodletting likely won't do a lot of harm but they absolutely won't help and can totally harm at higher amounts.
Yeah...that's kind of how most of the food combining claims stack up against modern knowledge of the human body and nutrition.
What We Know About Digestion
Remember that one way street digestion analogy I shared that's commonly used to describe why food combining is important? Well - it's not a great analogy. It's pretty bad, actually. Human digestion doesn't work like a one-way street. In actuality, it's more like a really busy many-lane highway system.
Food combining tends to oversimplify digestion. It seems like a lot of proponents visualize food hitting the stomach in a neat orderly fashion with each individual food waiting it's turn to be digested and passed to the small intestine, like this:
When in actuality, even when food first hits your stomach it's more like this:
That's because digestion actually starts in our mouth. Your teeth and tongue work together to start mechanically breaking down the food. As this is happening, the food mixes with saliva, which contains some digestive enzymes (salivary amylase, lysozyme, and lingual lipase). Yep - digestive enzymes are at work and digestion is already well underway before the food has even left your mouth.
Once in the stomach, the strong stomach muscles work to continue breaking the food down further. This physical churning is combined with the release of stomach acid and some digestive enzymes to create chyme - a pulpy, acidic fluid made up of all the stomach juices and partially digested food.
This brings us to the intestines. Let's start with the first part of the small intestine, the duodenum. Chyme is slowly released into the small intestine along with digestive enzymes from the pancreas (to help break down fat, carbohydrate, and protein) and bile (produced in the liver, stored and secreted from the gallbladder and works to help digest fat).
After the duodenum, digestion continues into the next parts of your small intestine: the jejunum (where further digestion creates even smaller molecules allowing for individual nutrients to be absorbed) and the ileum (the longest part of your small intestine where nearly all nutrients are absorbed through the intestinal wall).
At the point all that is left is mostly water and waste (i.e. plant fiber, dead cells shed from your digestive tract). This is pushed through the large intestine, where water is absorbed and the waste eventually becomes a bowel movement.
You Don't Really Want Fast Digestion
Remember how we talked about one of the claims of food combining is that it improves digestion by making it faster and more efficient?
When digestion happens too fast, diarrhea happens. And that's not an optimal or normal regular bodily function.
Fiber is something really important to our health, but it actually slows our digestion. Here's why that's a good thing:
- Slower digestion means slower transit time through your system, which means more time for your body to absorb nutrients.
- With slower digestion, the fiber occupies your digestive system longer, which gives a greater sense of satiety or fullness longer. This can help sustain hunger levels throughout the day and promote weight maintenance and even weight loss.
- Fiber slows the absorption of blood sugar to your body, preventing a sharp spike then quick drop of blood glucose. If you've ever had just a cup of juice alone versus a cup of fresh berries, you may have been able to notice this difference firsthand.
- Remember the waste products we talked about in digestion and the large intestine? Plant fiber is a big part of waste, and plays a big role in regular bowel movements which is beneficial to digestion and gut health.
Why Food Combining Rules Make Zero Sense
When it comes to the food combining rules, I struggle to find any remote logical basis based on what we currently know about food and nutrition, compared to hundreds of years ago.
For instance, let's look at protein. You can consume protein on a food combining diet, you just can't consume protein and fat together. But what about eggs, salmon, chicken, shrimp, pork, beef, etc.? Even in the leanest animal proteins, there is still some fat.
Okay, well what about plant proteins? Nope - because the majority of plant proteins also contain carbohydrates. Beans, tofu, tempeh, soy...nope, none are an exception.
Additionally, protein isn't just limited to foods typically labeled as protein foods. Starches? They all have protein - even starches like pasta often have around seven grams protein per serving (and I'm talking regular, semolina wheat flour pasta, not even a legume-based or protein-enriched pasta). Vegetables? Have protein. Even non-starchy, fiberful veggies like artichokes and broccoli and leafy greens - they all have protein.
Even the rule of eating fruit on an empty stomach - okay, not that big of a deal for a healthy individual, but for an individual with with blood sugar concerns, this could be problematic, causing dramatic spikes in blood glucose fluctuation that may be a lot harder for their body to deal with, with potentially damaging effects.
Also, I want to note that sometimes nutrient absorption is actually increased by combining different foods! Example: fat-soluble vitamins (often found in things like protein and leafy greens) actually should be consumed with fat for your body to better absorb them.
Alkaline vs. Acidic Foods and Body pH
The dietary effect of consuming different pH foods has minimal effect on bodily systems. Sure, after eating something with a more acidic pH, like steak, urine may have a more acidic pH in the few hours after eating. But in a healthy individual, that's just your body maintaining homeostasis. Ultimately the pH of different systems in our body have a lot of checks and balances to ensure they run as they're supposed to. Stomach acid is needed for digestion and is highly acidic - but that's necessary to digest foods. Blood pH has a very specific range that is pretty hard to move, for good reason - large deviations to blood pH would be fatal.
Also, to note, one of the beliefs of pH food combining is that carbohydrates should be eaten alone/ not with protein-rich foods, because it's theorized that the highly acidic stomach acid prevents carbohydrate digestion. Amylase (the digestive enzyme for starches) is hypothesized to be less effective in more acidic environments. But in reality, our bodies are pretty smart and know what they're doing.
Salivary amylase is released in our mouths when we first start tasting and chewing starch, like a piece of bread. Some studies suggest 80% of starch is broken down by salivary amylase alone. Once in the stomach, pepsin (protein digestive enzyme, tolerant to highly acidic environment) starts breaking down the protein consumed - which is great since even high starch foods, like bread and pasta, also contain protein! Then once released into the small intestine, the pancreas releases pancreatic amylase (and other enzymes) to further help breakdown and digest starch.
The graph above is a great visual from this study.
Even older studies from the 90s were already showing that gastric acids aren't as damaging to amylase activity as once thought.
Basically - there is zero physiological reason why our bodies can't digest multiple macronutrients at the same time. In fact, for a healthy person, you're likely going to have a more satiating, nutritious, and enjoyable meal by enjoying all three macronutrients at once.
Food Combining and Weight Loss
The one study that I found about food combining showed that there was zero difference in weight loss and results between the test group (the food combining group) and the control group (a balanced diet with the same calories and macronutrient distribution, just not consumed according to food combining rules).
Anecdotally, you'll hear stories how people found weight loss success with food combining. My hunch is that food combining "works" as a weight loss diet for some people because of a few reasons:
- It brings a greater awareness to what you're consuming. If someone has previously never really thought about their food or health or tracked what they ate, they're likely going to be more conscious of their dietary decisions just through this increased awareness.
- They're likely eating more vegetables. Think about it: if you can't have protein and starch or protein and fat together, but you can have starch or protein or fat with non-starchy vegetables, most people will find themselves eating more non-starchy vegetables to help fill up. If someone's plate typically was 50-100% starchy carbohydrates, protein, and fats (not bad foods by any means, just more energy/ calorie-dense foods), but now 50-75% of their plate is non-starchy vegetables, their meal is likely going to have less calories than it did before.
- With food combining, you're supposed to wait a few hours before "switching" foods. So, if you have protein at lunch, you should wait at least 3-4 hours before "switching" to starch. For people inclined to snack on starches, timing dictates you have to wait, so if you truly need to snack for hunger, you're only really allowed to eat non-starchy vegetables again. For people inclined to snack on sweets (even fruit!) sugar and fruit must be consumed on an empty stomach. So if you normally are one for sugary or starchy snacks or beverages in the afternoon or evening out of boredom, loneliness, stress, or any other emotion, food combining doesn't allow this.
Personal Experience Isn't Invalidated
We all have our own personal experiences. I know there are people who swear by food combining and that it works for them. The same thing can be said for proponents of literally any diet.
If you are eating enough, if you do not feel deprived, if you're not making yourself crazy or sacrificing your mental health with the rules, and if this is truly sustainable for you to do for the rest of your life and you find yourself better off from it - great, keep doing what works for you.
My intention here isn't to invalidate your personal experience. My intention is to look at science and evidence and help break down different diets and information in a way that helps cut through the confusion to help people make more informed decisions about their diet and health.
It's also really important to talk about this because there are wellness "professionals" and influencers who are actually selling programs and making money using food combining - and this is damaging to the product, it's wrong, it's not factual, and it's actually illegal, too.
Food Combining Final Thoughts
Based on our modern knowledge of the human body and science of nutrition, I think it's pretty clear that the food combining diet isn't necessary or science-based. In fact, it's actually quite outdated when you look at the science.
I'm concerned that the amount of rules (that make no physiological sense and science proves pointless) may lead to unnecessary obsessive thoughts around food, unnecessarily overcomplicating food and nutrition, and potentially more unsustainable yo yo dieting. At best, food combining could lead to some frustrating mealtime experiences, but at worse it could lead to obsessive thoughts and food morality that may fuel disordered eating and even eating disorders for some.
Everything is individualized, but a healthy, balanced diet absolutely does not have to center around arbitrary rules and complications like outdated food combining does.
If you have any questions about your personal health and nutrition, talk to your doctor and/ or find a dietitian to work with like myself. While research-based, this article is designed to be purely informative and does not substitute for individual medical and nutrition advice.
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