Functional medicine: Focusing on imbalances in core metabolic processes

The remainder of this article focuses on the evidence behind a subset of FM treatments, which typically include various dietary interventions (elimination, cardiometabolic, detox) and multidomain lifestyle modifications. The practitioner’s selection of dietary interventions, nutraceuticals (vitamins, minerals, essential fatty acids, botanicals), and probiotics is informed by results of different diagnostic tests.

Nutrition and supplements

Nearly one-third of older Americans are affected by at least 1 vitamin deficiency or anemia, and even those consuming an adequate diet have a substantial risk of any deficiency (16%), although less so than those with an inadequate diet (57%).¹⁷ The Western diet is known to be nutrient deficient, particularly in vitamin D, thiamine, riboflavin, calcium, magnesium, and selenium.¹⁸ Dietary supplement nonusers have the highest risk of any deficiency (40%) compared with users of “full-spectrum multivitamin-multimineral supplements” (14%) and other dietary supplement users (28%).¹⁷

Common FM tests are MTHFR genotyping, comprehensive stool profiles, hormone and heavy metal panels, allergy panels, lactulose breath testing, and micronutrient and advanced lipid panels.

Nevertheless, the US Preventive Services Task Force (USPSTF) concluded in 2014 that there are not enough data to make a recommendation for or against taking vitamins A, C, or E; multivitamins with folic acid; or combinations of these vitamins for the primary prevention of CVD or cancer.¹⁹ USPSTF also does not recommend daily vitamin D and calcium supplementation in community-dwelling, postmenopausal women for primary prevention of fracture.²⁰ Notwithstanding the lack of supplement recommendations for primary prevention, their benefits in patients with chronic disease is still being investigated. For example, a polyphenol-rich antioxidant may reduce cardiovascular complications in those with diabetes.²¹

Rethinking how nutrition studies are designed. Drawing on studies to determine the benefits of nutrition in chronic disease has been challenging. Factors that must be taken into account include the types of vitamin and mineral supplements patients use, nutrient absorption and utilization, and differing dietary assessment methods and reference values used.¹⁸ For example, vitamin and mineral absorption work best with whole food or fortified diets wherein specific nutrients are consumed together (eg, vitamin D and vitamin E with fat; non-heme iron with vitamin C).^22-24 Foods with competing nutrients or “inhibitors” may even require absorption enhancers at minimum molar ratios.²⁴

Adding to the complexity of vitamin and mineral absorption, botanical dietary supplements have their own modifying effects on micronutrient absorption.²⁵ These are just some of the reasons randomized controlled trials (RCTs) are fundamentally limited when investigating the health outcomes of diet and supplementation, and alternative study methods should be considered for future nutrition clinical trials to better inform clinicians who are prescribing supplements.²⁶ In the meantime, nutrition plans can be individualized to patients’ biological and cultural needs, ideally in conjunction with a multidisplinary team that includes dietitians, behaviorists, and exercise specialists.²⁷

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