Nutrition Notes

You Aren’t What You Eat, You’re What You Absorb

As a healthcare professional who understands the critical role of a healthy diet, you’re likely already sharing tips with your patients about optimizing nutrient intake, whether they follow a Paleo style diet, a ketogenic diet, or prefer to stay plant-based. Their food choices are probably very good, but there’s a missing piece that’s rarely talked about and which might help them get even more bang for their nutritional buck: improving nutrient absorption.

The adage “you are what you eat” makes for a nice sound bite, but it’s incomplete. We’re not what we eat, but what we digest and absorb. With this in mind, there are a few simple tips that can help people make the most of the high-quality foods they buy.

Something that’s obvious to most functional medicine and nutrition practitioners but which is much less appreciated by our patients is eating in a calm, unhurried atmosphere and with a relaxed frame of mind. Many stereotypes are based in at least a small kernel of truth, and the images of harried, stressed-out executives wolfing down lunch on the go and popping antacids between meetings is a good example. When the sympathetic nervous system’s fight or flight mechanism is engaged, the parasympathetic’s rest and digest doesn’t stand a chance.

Being realistic, it’s not always possible to enjoy a slow, serene meal surrounded by bamboo trees and gently babbling brooks. For the times when digestive function might be compromised by stressful circumstances or by gastrointestinal conditions that hinder nutrient absorption, supplementing with HCl, ox bile, and/or digestive enzymes may be helpful.

Moving on to issues patients might not be aware of, certain nutrients and various compounds affect the absorption of key minerals. This information can help them make better choices when combining certain foods, beverages, and supplements. For example, alcohol generally increases the absorption of iron, but polyphenols in red wine inhibit non-heme iron absorption. (Unlike the non-heme iron found in plant foods, the heme iron in animal foods, including shellfish, is not typically affected by other compounds.) Polyphenols and tannins in foods and beverages such as cocoa, coffee, black tea, walnuts, blackberries and blueberries may reduce non-heme iron absorption.

Calcium may also interfere with iron absorption, and is the only substance known that inhibits absorption of both heme and non-heme iron. (Individuals taking iron supplements may be advised to take them at least two hours apart from calcium-rich foods or supplements.) On the contrary, vitamin C is well-known to enhance non-heme iron absorption, with the enhancement of iron absorption from vegetarian meals being directly proportional to the quantity of ascorbic acid present.

Decreased non-heme iron absorption is only one example of the many ways in which various food compounds can interfere with nutrient absorption. The presence of phytic acid or oxalic acid (phytate and oxalate) also interferes with nutrient bioavailability, particularly that of calcium, manganese, magnesium, iron and zinc. This is important for patients to know, because those who are still consuming whole grains and those who choose to include legumes in their diet may not be getting all the nutrients they think they are. The amounts listed on food labels and those provided by food tracking apps typically don’t account for limited bioavailability in the presence of antinutrients.

The negative effect of certain antinutrients on nutrient absorption can be reduced via traditional preparation methods such as soaking, sprouting or fermentation. Those who consume whole grains may wish to look for (or bake at home) breads and other grain products made from sprouted wheat, rye or other grains. Sourdough bread made from dough subjected to an extended fermentation period may have, allowing for better bioavailability of magnesium and other minerals.  

Apart from phytic acid in whole grains and legumes, there are other foods typically considered wholesome and nutritious, but which may not deliver their full complement of nutrients owing to the presence of oxalate. The short list includes spinach, zucchini, kale, celery, collards, cocoa, figs, raspberries, blackberries, beans, black tea, and most nuts and nut butters. (See here for a complete list of high, medium, and low-oxalate foods.) Foods contain both soluble and insoluble oxalate, with soluble being better absorbed than insoluble. Boiling can reduce soluble oxalate content by as much as 30-87%, and steaming by 5-53%. The key would be to not consume the water left behind, such as in a soup or stew. Soluble oxalate absorption is reduced with co-ingestion of calcium-rich foods, so creamed spinach isn’t only delicious; it’s a way to reduce the absorption of problematic oxalates.

Last, but not least, we cannot ignore the role of pharmaceutical drugs in altering nutrient absorption. For example, long-term use of proton pump inhibitors and other acid-suppressing or neutralizing drugs is associated with increased risk for deficiencies of iron, magnesium, and B12. The popular drug metformin is known to induce low B12 levels in patients with type 2 diabetes.

Drugs can increase, decrease, or prevent intestinal nutrient absorption. Regarding use of nutrients, drugs can speed the metabolism of particular nutrients, resulting in higher dietary requirements for those nutrients, and drugs may also increase excretion of certain nutrients, also potentially increasing the dietary requirement. Patients should be made aware of these issues for any medications they’re taking so they can take precautions to time the intake of certain foods away from the medication, or to establish an effective supplement regimen if warranted.  

Buying and cooking wholesome, unprocessed, nutritious foods is the foundation for a healthy diet. The next step is for patients to give thought to constructing meals with combinations of foods that will maximize absorption of the high-quality foods they’re taking time to prepare.