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Food combining is a loose term that has circulated within some nutrition and diet circles to suggest that the best results come when certain foods are eaten together. Along similar lines, there are specific food types (or macronutrients) not to be eaten together due to anecdotes of potential digestive distress or changes in metabolism. For example, an internet search on “food combining” will lead to various websites talking about which foods “mix well” and which foods “do not mix well”. As shown in the graphic below, fats and proteins would not mix well, nor would protein and starches or starches and fruit. However, vegetables and fruit, vegetables and fat, and vegetables and starches would all be food combinations seen as “mixing well”.
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It’s difficult to find the point of origin for the food combining philosophy as it is not found to any great extent in scientific literature. Some suggest that food combining may have potential roots in Ayurveda, a traditional medicine system in India. Besides focusing on disease prevention, diagnosis, and treatment, Ayurveda offers individualized nutrition guidance, including optimal food combinations. According to Ayurveda, foods that are not complementary can cause indigestion, gas, acidity, and the formation of toxins. However, when eaten separately, the same foods can support proper digestion (“agni”). Properly paired food groups are said to work in harmony, promote good digestion, and support optimal absorption of nutrients. According to Ayurveda, certain foods, such as milk and melon; milk and sour fruits; or honey and ghee in equal quantities are incompatible.
In some schools of thought, foods may be labeled as acidic or alkaline to specify food combinations further. Food combining is also seen in dissociated diets, which entails spreading the intake of carbohydrates, fats, and proteins throughout the day and, more specifically, abstaining from ingesting carbohydrates and fats together.
Does Science Support Food Combining?
Foods are inherently complex mixtures of compounds. Food synergy is the idea that relationships between different constituents in food, such as specific nutrients or macronutrients, are significant and even coordinated. Nuts provide an example of this concept as they contain potentially unstable unsaturated fatty acids and antioxidants to protect against them. Viewing foods as a whole rather than as single food components can offer valuable insights into their impact on health. This idea is demonstrated in peanut allergies, in which researchers have shown that a peanut’s food matrix may enhance the immune response compared to purified peanut allergens alone.
Similarly, some food combinations synergistically or antagonistically impact total antioxidant capacity. Researchers sought to investigate these interactions among twenty commonly consumed foods, including fruits, vegetables, meat, dairy products, grains, nuts, seeds, and beverages. In the study, samples were first freeze-dried and ground before individual total antioxidant capacities were measured. Then they were subjected to in vitro digestion, including simulated salivary fluid, gastric fluid, and duodenal fluid. Food interactions and their resulting total antioxidant capacities were categorized into synergism, antagonism, and additive interactions. In a synergistic interaction, there was a more significant overall effect when combined. An antagonist interaction resulted in a lower overall effect when combined. And an additive interaction resulted in a net effect.
Synergistic effects were seen between breakfast cereal with fruit and breakfast cereal with hazelnut. Meanwhile, an antagonistic effect was observed between breakfast cereal and milk. Milk also interacted antagonistically with fruits, seeds, and whole wheat bread. Whole wheat bread interacted synergistically with green and black tea but antagonistically with flax, chia, and sesame seeds. These results show how certain food combinations can result in greater total antioxidant capacity and lesser total antioxidant capacity.
Additionally, the aforementioned study simulated the digestive process with various digestive fluids to measure changes in the total antioxidant capacity of certain foods at different stages of digestion. Researchers found that different conditions in the digestive system significantly affected the total antioxidant capacity of foods. For example, antagonism was observed in breakfast cereal with flaxseed under gastric conditions, but synergism was observed under intestinal conditions.
But can food combinations improve digestion, and do foods need a certain potential of hydrogen (pH) for absorption? While the importance of pH during digestion is valid, the reality is that food particles are exposed to various conditions as they travel through the digestive tract. In the stomach, food is subjected to hydrochloric acid that begins protein breakdown, kills microorganisms such as bacteria and parasites, and aids in the absorption of iron, vitamin B12, and calcium. As food moves into the small intestine for further digestion, bicarbonate is released as a component of pancreatic secretions, which has a protective mechanism against gastric hydrochloric acid. Bicarbonate is alkaline and has a neutralizing effect against stomach acid, allowing pancreatic enzymes to function optimally. However, even in the stomach’s acidic environment, bicarbonate is secreted, most likely to protect the stomach against acid.
Therefore, while pH is an important factor in digestion, the body automatically facilitates this process in most individuals. While that is the case in individuals with healthy digestion, there are some instances where digestive processes are not optimal. For example, some individuals may experience achlorhydria, in which there is reduced or absent hydrochloric acid in the stomach, often due to an underlying medical condition such as hypothyroidism or H. pylori infection. Even the simple, everyday occurrence of stress could alter the gastrointestinal tract. Therefore, it may seem plausible that there could be select groups of individuals with known digestive conditions who may benefit from eating foods away from others.
Another concern that appears to be shared in those who follow the food-combining approach is that if foods digest at different rates, there can be indigestion, leading to gas and bloating from fermentation. However, the entire digestive process can take between 10-73 hours, meaning that several meals will be processed simultaneously. Moreover, the fermentation of dietary fiber is beneficial to human health as it creates short-chain fatty acids (SCFA) in the colon, which have several health benefits due to their anti-inflammatory and immunoregulatory activities. Regarding gut health, food combinations such as fruit and yogurt have a potential synergistic effect thanks to their prebiotic and probiotic content, respectively. Combining prebiotics and probiotics can enhance the survival of probiotics as they travel through the digestive system and further modulate the microbiota.
Finally, based on what one might find on the internet, the food-combining trend appears to have a weight loss focus. However, there has been only one study comparing a food combining or “dissociated” diet to a balanced diet for weight loss. This was an in-hospital, 6-week study involving 54 obese participants who were randomly assigned to one of two groups: a dissociated diet or a balanced diet. Energy intake was matched between both groups (1100 kcal/day), and macronutrient intake was similar. Each group experienced significant weight loss, but there was no difference between the two diets.
Are There Benefits to Food Combining?
There are instances when food combining makes sense. For example, combining non-heme iron with vitamin C enhances iron absorption, such as consuming lentils with bell peppers or spinach with lemon. In addition, the combination of calcium and vitamin D increases bone mineral density in postmenopausal women. Another example of a synergistic food combination is turmeric and black pepper. Turmeric contains the polyphenol curcumin, known for its antioxidant and anti-inflammatory effects but has low bioavailability. Curcumin’s bioavailability can be increased by as much as 2000% when combined with piperine, the active component of black pepper. Macronutrients can also aid nutrient absorption. For instance, combining dietary fat with orange vegetables, such as carrots and butternut squash, can enhance carotenoid absorption and the potential for bioconversion into vitamin A.
On the other hand, certain nutrients inhibit the absorption of others. For example, calcium can inhibit iron absorption. However, it has also been found that sufficient amounts of foods that enhance iron absorption (e.g., vitamin C) can overcome inhibitors of iron absorption (e.g., calcium).
One potential benefit of the food-combining diet is that it appears to encourage the consumption of non-starchy vegetables, which provide health-promoting vitamins, minerals, fiber, and phytochemicals. As of 2019, only 1 in 10 U.S. adults met vegetable intake recommendations.
So while there are benefits to combining (or avoiding combining) certain foods, they are not necessarily parallel to the goals of the food-combining diet, which appears to lack scientific evidence at this time.
What are the Downsides of Food Combining?
It possibly restricts dietary diversity. Unless adequately planned, excessive rules around food combinations can feel limiting, which may decrease diet diversity and opportunities for synergism among foods. A study involving Puerto Rican adults in Boston found that fruit and vegetable variety – but not total fruit and vegetable intake – was inversely associated with inflammation, highlighting the importance of consuming a variety of plant foods.
It may not be a sensible or sustainable diet. Adhering to strict food combining rules can be difficult and interfere with essential aspects of life. Not only does food provide nutrition to the body, but it’s also involved in social contexts as it creates bonds between people, is a component of culture, and even helps construct a person’s identity. Strict eating guidelines can interfere with these aspects, making it difficult to share meals with others, experience culture, and express oneself. Notably, the Mediterranean diet is well-studied for its health benefits and emphasizes enjoying meals with others and being socially active.
Orthorexia risk. Orthorexia nervosa is an eating disorder in which someone is obsessively focused on healthy eating and has a resulting inflexible diet. Stress and anxiety accompany these dietary restrictions. Restrictive therapeutic diets for digestive disorders may increase the risk of developing orthorexia as seen in a review of the literature available on orthorexia in gastroenterology. The review showed a heightened risk of developing orthorexia in those who follow a diet for digestive issues or food intolerances. Therefore, those using food combining to alleviate digestive issues should be aware of this potential risk.
Final Remarks
At face value, the practice of food combining appears to encourage the consumption of minimally-processed foods and non-starchy vegetables. However, it’s likely to limit an individual’s food and meal composition choices, which can decrease diet diversity, reduce the synergistic effects of foods, and impact other aspects of their lives, including relationships with others and cultural experiences. The eating style best for you is a personalized approach that includes your health needs, culture, and food preferences. If you have questions about which foods or eating patterns can best support your health, talk to your doctor, nutritionist, dietician, or another healthcare team member for personal options based on your circumstances.
