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Ultimate personal diet plan? Follow your genes

| February 22, 2016

We all wish we we could eat whatever they want while maintaining a healthy weight. But that lifestyle seems to elude all but a few. The phenomenon, and its converse, seems to run in families, suggesting a possible genetic component that has been extremely difficult to prove. Even the most well-studied body weight gene, FTO, only accounts for a few kilograms of variation in human body weight. That’s nowhere near enough to explain obesity. So scientists are now examining how our genes, the microbes in our guts, and what we eat all work together to affect how our individual bodies absorb nutrients, store fat, or deal with extra calories.

A spate of recent stories have sung the praises of the new field of nutrigenomics — the field which explores how food affects gene expression — despite the fact that the science is very new and studies conducted so far have used very small sample sizes. The Daily Mail even called nutrigenomics ‘the holy grail’ for chronic dieters. But the science is far from complete. At this point we are just beginning to get a grasp on how much variation there actually is in human responses to food.

In a large study published in Cell, researchers tracked 800 people’s blood sugar response as they ate a variety of foods. A higher blood sugar bump after eating is related to fat storage in healthy bodies. The results were remarkable. Individuals responded to different kinds of foods in ways that were non-standard and not predicted from the glycemic index of the food. The variation between people was remarkable, too. This figure, showing two participants’ responses to a banana or cookie is a great example:

bananacookie
Comparing blood glucose levels of 2 participants. Yellow line is after eating a banana, blue is after eating a cookie

We know there are big swings in an individual’s biology, but the causes of those swings is still largely unknown. Earlier studies have suggested a role for gut bacteria in weight and metabolism and the authors of the Cell study also examined the role of gut microflora (the bacteria living in a person’s gut) of their test subjects. Their data seem to corroborate earlier findings of a link between gut microflora and an individual’s glycemic response, but this is just part of the story. Still most science into the gut microbiome still can’t place whether the microbiome changes caused or were caused by obesity.

Other researchers are looking at human genetics to solve the puzzle of why people respond differently to foods. There is some established basis linking genes and nutrient metabolism writes Kate Murphy at the New York Times:

Scientists are beginning to tease out the connections. Studies have linked at least 38 genes to nutrient metabolism — variants of which are thought to hinder or help absorption or the efficient use of nutrients in foods. Depending on your genetic makeup, studies suggest you might want to consume more or less folate, choline, vitamin C, fatty acids, starches and caffeine.

But knowing what variants a person has for those established genes is unlikely to provide enough information to piece together a personalized diet plan. And there are likely to be hundreds more variables involved. That’s good news for companies like Vitagene who look at a person’s genome and recommend a slew of supplements based on their genetic screens. But even if hundreds of candidate genes are discovered, there will will be differences that can’t be explained says Aaron Krumins at Extreme Tech:

Further complicating the situation is that even after discovering that genetics plays a crucial role in the metabolism of various substances and foods, much of the genetic components remain unidentified and stubbornly resistant to investigation. For instance, it might be that a twin study demonstrates genetics account for 80% of one’s ability to metabolize caffeine, but of that 80%, only 10% can be accounted for by the current genome-wide association studies. This missing 70% is an example of what geneticists refer to as the “missing heritability problem.”

Although rates of obesity increase have slowed among some parts of the U.S. population, they have grown rapidly in other parts of the world according to the World Health Organization. And currently there are no great and long-lasting treatments for obesity. While it is possibly for many people to lose weight in the near-term with lifestyle changes, weight loss is notoriously difficult to maintain for reasons experts don’t really understand. Because of the myriad of diseases associated with obesity, we need better treatment option. And if people see greater results by avoiding foods or making exercise changes informed by their genetics, that might help them attain and maintain weight loss.

Related article:  Epigenetic Zs: Could a bad night's sleep alter your genes?

Some experts worry that telling a person that they are overweight because of their genetics will dissuade them from making diet and exercise changes. But research suggests that’s not likely to happen. Molly Bray, who studies Nutrigenomics at the University of Texas at Austin, told the Daily Mail:

When people hear that genes may be playing a role in their weight loss success, they don’t say, “Oh great, I just won’t exercise any more.” They actually say, “Oh thank you. Finally someone acknowledges that it’s harder for me to work than it is for others.” And then I think they’re a little more forgiving of themselves, and they’re more motivated to make a change.

Meredith Knight is a contributor to the human genetics section for Genetic Literacy Project and a freelance science and health writer in Austin, Texas. Follow her @meremereknight.

The GLP featured this article to reflect the diversity of news, opinion and analysis. The viewpoint is the author’s own. The GLP’s goal is to stimulate constructive discourse on challenging science issues.

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