February 15, 2017 – Precision medicine—tailoring drugs and therapies to a person’s genetic profile—has been touted in recent years as a way to maximize the benefits of treatment while minimizing side effects. Experts are now wondering if personalizing an individual’s diet according to their DNA profile—called precision nutrition—can also improve health.
Frank Hu, professor of nutrition and epidemiology and chair of the Department of Nutrition at Harvard T.H. Chan School of Public Health, tackled the topic before a standing-room-only crowd in Kresge 502 on February 8, 2017.
With the cost of sequencing a human genome now about $1,000—down from a staggering $100 million in 2001—incorporating genetic information into either medical treatment decisions or nutrition advice is increasingly feasible, said Hu. Some companies have already started to market personalized “nutrigenomics” analyses to consumers. Such analyses can reveal how an individual may respond to everything from sodium to saturated fat to whole grains to caffeine. But with little data available on nutrigenomic testing, the jury’s still out on whether it can actually lead to improved diet quality or better health outcomes, Hu said.
He cited some recent studies that offer a glimpse into precision nutrition’s potential:
Personalized diets to smooth blood sugar spikes
There is wide variability in how much people’s blood sugar spikes after meals, which makes it difficult to offer one-size-fits-all nutrition advice. In a 2015 study, researchers analyzed data from 800 study participants—including data on gut microbiota, which play a key role in diet and health—and developed an algorithm that predicts how much an individual’s blood glucose level might increase after a particular meal. The results showed that a dietary intervention based on the algorithm helped participants significantly lower their typical post-meal blood sugar spikes.
“While using an algorithm to design a personalized diet to lower blood sugar is interesting,” Hu said, “it is unclear whether it has the same benefits on other health outcomes like blood cholesterol or can be applied to other populations who have different dietary and lifestyle habits.”
The buzz about coffee
Many epidemiological studies have suggested that coffee is beneficial to health outcomes like type 2 diabetes; more recently, genetic analyses have shed light on the biology behind coffee’s health effects. A genome-wide association study by former Harvard Chan research associate Marilyn Cornelis uncovered eight genetic variants related to coffee consumption, some related to caffeine metabolism, Hu said. “Some people are fast metabolizers, some are slow—that determines how much coffee you drink and what response you have after drinking coffee,” he said. Other studies using transcriptome and proteome profiling—analysis of messenger RNA molecules or gene readouts and proteins, respectively—have found gene expression and protein biomarkers related to coffee’s anti-inflammatory qualities and anti-diabetic effects.
“These types of analyses can help us identify individuals who may benefit from increasing or decreasing coffee consumption,” Hu said. “And this type of approach can be applied to other beverages, other foods, or food patterns.”
Gene and diet interactions
Several recent analyses have focused on gene, diet, and lifestyle interactions, based on three large cohort studies—the Nurses’ Health Study, the Health Professionals Follow-up Study, and the Women’s Genome Health Study. A 2012 study led by former Harvard Chan assistant professor Lu Qi showed that people carrying more obesity gene alleles were more susceptible to increases in body mass index from drinking sugar-sweetened beverages than were those with fewer obesity gene alleles. The study also suggested that regular sugary beverage consumption may actually amplify the genetic risk of obesity. On the other hand, said Hu, another 2012 study led by Qi showed that a healthy lifestyle such as increasing physical activity may mitigate the genetic risk of obesity.
“The interplay between genes and diet indicates that genes are not destiny, and individuals can offset their obesity genetic predisposition by following a healthy diet and lifestyle,” Hu said.
Microbiota and obesity
In a 2013 study that Hu called “fascinating,” researchers transplanted gut microbiota—essentially, fecal matter—from an obese human twin into a group of lean mice. Into another group of lean mice, they transplanted microbiota from a lean human twin. Both groups of mice were fed the same diet. The first group—the mice that got the transplant from the obese human twin—became obese. The other mouse group stayed lean.
“This suggests that gut microbiota may play an independent role in obesity,” Hu said. “The question is, can we do this in humans—do fecal transplants from a lean person to an obese person?” He said that randomized clinical trials are already underway in humans to see if pills containing freeze-dried fecal matter can treat obesity. Other studies have looked at how gut microbiota may impact diabetes and cardiovascular disease. Said Hu, “These findings may provide novel prevention and therapeutic strategies such as probiotics and prebiotics for metabolic diseases.”
Metabolite signatures of diet
Scientists are also using sophisticated analytical techniques to learn more about metabolites—small molecules that are products of metabolic reactions in cells. The analytic techniques are known as “metabolomics”; a person’s “metabolome” is the entirety of metabolites in his or her body. Some studies have shown that certain foods and certain diets have unique metabolic signatures, and researchers are beginning to assess the relationship between these signatures and diseases such as diabetes and cardiovascular disease. For example, in a 2016 study, Hu and colleagues from Spain found that a Mediterranean diet enriched with extra-virgin olive oil or nuts reduced deleterious effects of blood metabolites such as branched-chain amino acids on cardiovascular disease.
Precision nutrition appears to hold a lot of promise, and it makes sense to embrace and harness new technologies and integrate them into epidemiological studies and dietary intervention trials, Hu said. But precision nutrition’s individualized approach means that it’s expensive and unlikely to have a broad impact on population health. On the other hand, public health efforts, including policies and laws, are focused on populations and aim at root causes of chronic disease such as socioeconomic inequities or unhealthy food environments. For that reason, Hu cautioned against overinvesting in precision nutrition research at the expense of public health efforts. “It should be a balancing act,” he said.
Learn more: The Nutrition Source
photo: Sarah Sholes