Using caution when making dietary recommendations based on RCTs

August 17, 2021   |   Evidence in Integrative Healthcare

Many, if not most, evidence-based dietary advice releys on less-than-gold-standard randomized controlled trial (RCT) data. Diet history from patients is most commonly used to determine what sorts of food combinations (daily diet) increase or decrease health outcomes. But these data are remarkably unreliable. Patients often tell investigators what they think they want to hear, not what actually is going into their mouths via diet histories.

The best RCT design compares interventions with known quantities of variables in the subjects. A recent randomized controlled clinical trial tried to quantify relationships between full-fat versus low-fat milk consumption on outcomes important for cardiovascular health.1Schmidt KA, Cromer G, Burhans MS, Kuzma JN, Hagman DK, Fernando I, Murray M, Utzschneider KM, Holte S, Kraft J, Kratz M. The impact of diets rich in low-fat or full-fat dairy on glucose tolerance and its determinants: a randomized controlled trial. Am J Clin Nutr. 2021 Mar 11;113(3):534-547. doi: 10.1093/ajcn/nqaa301. PMID: 33184632; PMCID: PMC7948850. The study looked at the result of consuming whole-fat milk products (yogurt, milk, cheese, etc.) versus low fat milk alternatives on glucose tolerance and its determinants in a patient population.

The trial was small, 72 subjects, all with metabolic syndrome, a cluster of conditions that occur together that increase the risk of heart disease, stroke and type 2 diabetes. Subjects were randomized to either full-fat milk products or low-fat dairy. Outcome measures were glucose tolerance, insulin sensitivity, pancreatic β-cell function, systemic inflammation, liver-fat content, and body weight and composition. The investigators hypothesized that the low-fat intervention would reduce the risk of heart disease.

However, the study concluded, “Contrary to our hypothesis, neither dairy diet improved glucose tolerance in individuals with metabolic syndrome. So in this small trial, restricting dietary fat intake in dairy foods did not change physiologic measures related to metabolic syndrome.

If you are making dietary recommendations to your patients, it would be good to keep in mind that some “evidence-based” nutritional advice is based on studies or research that are not considered high-quality. Consider limiting recommendations that are derived from extremely small sample populations or rely solely on study participants to self-report.