The Digestibility Dilemma: Should the food we eat be digestible?

Should the food we eat be digestible?

It seems like a simple question with an obvious answer. The purpose of food is to nourish our bodies with essential macronutrients (carbohydrates, protein and fat) and micronutrients (vitamins and minerals), and we can only access the nutrients in food if we are able to digest it. Indeed, historians point to the advent of cooking as a huge evolutionary leap for human beings; the improved digestibility of cooked foods may have been the nutritional jolt required to develop our bigger, energy-intensive brains. Considered in this context, digestibility is a very important attribute of our diets.

But consider this: Humans have a particular "organ system" (of sorts) that is essential to our good health. It has been shown to play a role in modulating our immune system – directing it to focus its efforts either outward against invaders or inward against our own selves; on our tendency to gain excess weight easily or with difficulty; on our risk of developing metabolic diseases such as Type 2 diabetes or cardiovascular disease. It appears to also play a role in our mental well-being, as well as the degree to which we experience pain. This mission-critical system is called our microbiome, and it's comprised of the trillions of microorganisms that inhabit our innards and outer surfaces – most notably, our intestines. And the primary way it gets nourished is by consuming the foods we eat but don't digest. Considered in this context, non-digestibility is also a pretty important attribute of our diets.

So ... to digest, or not to digest? That is the question.

The answer, of course, is both. The optimal diet would contain some easily digestible foods to feed our human cells the essential nutrients they need to function properly, as well as a variety of less digestible foods both to feed our non-human cells and help ensure we don't go overboard on the calories. And if you accept this premise, it becomes clear how dietary dogmas on the extreme of either position fall short.

The consequence of completely digestible diets typically expresses itself in terms of obesity and a lack of diversity and resilience in our gut's ecosystem. A highly digestible diet looks like this: eating only cooked foods with no roughage at all; choosing only animal proteins without any fiber-containing plant proteins such as beans, nuts or seeds; drinking fiberless fruit and veggie juices instead of whole fruits and vegetables; and consuming highly processed breads, cereals, grains and snacks formulated refined flours, starches, fat and sugar. Dietary patterns that swing too far toward this side of the pendulum risk overfeeding our human cells and underfeeding our microbial cells.

The consequences of highly indigestible diets – such as fully raw diets, and particularly raw vegan ones – can often be a state of malnutrition. In such circumstances, the body may find itself unable to maintain certain basic functions such as regulating body temperature, preserving bone and muscle mass, mounting an immune response against circulating pathogens or sustaining a menstrual cycle for women. The most nutrient-dense foods in the world may not actually be nourishing at all if the body cannot access the protein and vitamins locked within a raw, impenetrable seed coat or enzymatically break down a plant-based carbohydrate because it hasn't been biochemically transformed by heat and moisture. When the majority of one's intake consists of raw, plant-based foods, it's likely that our cells will lack adequate supply of essential calories, protein, vitamin B12, calcium, zinc and iron. Dietary patterns that swing too far to this side of the pendulum may feed our microbial cells quite well as they starve our human cells.

When we consider the importance of both digestibility and non-digestibility in our diets, some of the scientific holes in prevailing food faddist arguments are exposed as well. For example, I've had dedicated paleo patients explain an aversion to beans to me in terms of their lack of digestibility; since so much of the carbohydrate and resistant starch in beans is not digestible by human enzymes, they claim, this must mean humans aren't supposed to eat them. As should be clear by now, it is precisely this lack of digestibility that make beans such a health-promoting food: They supply some energy in the form of calories but not too much easy energy, like starchy white rice and potatoes, so as to promote high blood sugar or obesity, and they offer a variety of different fibers to nourish the multitudes of species who inhabit our guts.

I've also encountered paleo arguments that take aim against phytates, a natural form of phosphorous found in beans, nuts and grains that impede iron and zinc absorption (somewhat). Haters claim that phytates are basically an "anti-nutrient" that prevents our bodies from absorbing anything good from the food and will inevitably lead to malnutrition. In reality, of course, huge epidemiological studies show time and time again that populations whose intake of (phytate-rich) beans/legumes, nuts, seeds and whole grains is highest typically enjoy a variety of health advantages – such as lower mortality rates and lower rates of cardiovascular disease – compared to populations whose intake is minimal. Clearly, then, something good is coming out of these phytate-rich grains and legumes.

Similarly, dedicated devotees of food combining refuse to eat fruit with a mixed meal because they worried about the meal slowing digestion down, such that the fruit will "ferment" in the gut. This fear is based on a premise that food fermenting in our gut is a somehow bad, toxic or otherwise undesirable outcome to be avoided. In reality, "fermentation" is just a fancy way of describing how bacteria digest carbs – and it's precisely what we want to happen when we follow a high-fiber diet to nourish the gut microbiome, whose health and resilience is so essential to our own. So, besides the fact that a fruit's ultimate digestibility is not impacted by what it's eaten with, the takeaway here is that the fermentable soluble fibers, seeds and sugars in fruit that elude digestion and absorption by our own cells will be put to terrific use in service of our health. Fear not the fermentation, nor shall you fear the farting that results from aforementioned fermentation. It's a side effect of healthy living.

Health benefits of non-digestible foods aside, there remains the issue of tolerance. As in, many people find the side effects of too much non-digestible food to be prohibitive. Symptoms often include gas pain, socially undesirable levels of flatulence, uncomfortable abdominal bloating or diarrhea. In such cases, there's typically a disconnect between foods that are objectively "good for you" as a human being and subjectively "good for you" as an individual eater. Indeed, this is the heart and soul of my clinical practice: helping patients identify the healthiest diet that they enjoy and can comfortably tolerate. For some folks, it may mean avoiding entire families of foods – such as cruciferous vegetables or beans or sorbitol-containing fruits – period. For others, it can mean consuming trigger foods in moderation – knowing what portions can be comfortably tolerated and eating them in these modest, prescribed amounts. Some patients use digestive enzymes – such as lactase or alpha-galactosidase (sold as Beano or Beanzyme) – to help improve the tolerability of foods with less digestible components. It can take a bit of trial and error to figure this all out, but it's important to make the effort to ensure you're consuming the most diverse, digestible/indigestible, healthy diet you can comfortably tolerate.

Copyright 2015 U.S. News & World Report

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