When it comes to dietary guidelines, we’ve learned that a one-size-fits-all approach doesn’t work for everyone, which is why the emerging field of personalized nutrition is becoming a hot topic among dietitians. Also known as “precision nutrition,” this approach aims to assess the unique attributes of an individual—their DNA, the mix of bacteria in their gut, their biochemistry and health history, among other factors—to create a unique dietary plan that’s better matched to how their body responds to foods.
People respond differently to calorie-reduced diets
We used to think that a calorie was a calorie—that regardless of whether a calorie came from an almond, a piece of chocolate cake or a grape, it would have the same effect on the person doing the eating, in terms of weight gained or lost.
Today, though, advances in nutritional science are helping us understand that due to differences in the gut microbiome, and other factors, not all people metabolize foods the same. And that, in turn, may affect how much weight an individual might lose on a particular diet.
“You can have two people eat exactly the same thing, and have a slightly different response,” explains Dr. Christopher Gardner, the director of Nutrition Studies at the Stanford Prevention Research Center. In other words, the size of a calorie deficit doesn’t always correlate well with the amount of weight lost. It may also depend on what they are eating.
Low-fat vs. low-carbohydrate: is one loss diet better?
To learn if it’s possible to predict which individuals are best suited to a certain weight loss diet, Dr. Gardner led a recent study published in Cell Reports Medicine. The study assessed the dietary intakes, microbiome composition, blood chemistry and other metabolic data collected from 609 people before, during and after a year-long weight loss trial.
Each participant was randomized to follow either a healthy low-fat diet or a healthy low-carbohydrate diet for one year; both diets were made up of mostly whole and minimally processed foods.
Strictly adhering to the assigned diet was what mattered most for successful weight loss during the first six months (short-term weight loss). But this wasn’t the case for weight loss at one year.
Within each diet group the range of weight loss over 12 months spanned a remarkable 88 pounds. For example, some lost 66 pounds while others, eating the same number of calories and the exact same diet, gained back 22 pounds they had lost in the first six months. Dr. Gardner’s team then tried to determine what accounted for such variable weight loss among participants in the same diet group.
“It’s not fair,” says Dr. Gardner. “We sat with these people…we said, ‘we can almost guarantee that some of you are going to be…looking across the table at someone who got exactly the same advice, and lost more weight than you.’”
The reason for the observed differences in weight loss may come down to how an individual metabolizes nutrients. Some people, Dr. Gardner believes, will lose weight more easily on a low-carb diet while others are more suited to losing weight on a low-fat diet.
The researchers identified several biomarkers of metabolism that predicted weight loss success among participants. These included the types of microbes living in their gut, specific proteins in their bloodstream and amounts of carbon dioxide they exhaled.
This discovery supports growing evidence that, in the not-so-far-away future, dietitians will be able to assess an individual’s unique dietary, molecular and metabolic factors to develop truly individualized weight loss plans.
How soon? Within the decade, Dr. Gardner believes.
In the meantime, focus on diet quality
There are other important takeaways from Dr. Gardner’s study. Short-term weight loss success was correlated to adhering to a high-quality diet. “The central themes were eating more vegetables and being really focused on fibre,” he says.
In the healthy low-carb diet group, participants who had higher intakes of vitamins C, E and K experienced greater weight loss. As well, low-carb dieters whose diets contained a higher proportion of unsaturated fat, especially monounsaturated fat, achieved more weight loss than those with higher intakes of saturated fats. This translates into a diet higher in vegetables, nuts, nut butters, avocados, olives and olive oil.
Among participants assigned to the healthy low-fat diet, a higher intake of whole grains and fibre was associated with enhanced weight loss. The results suggested that eating whole grains, fruits and beans and lentils – while limiting refined starches and added sugars – may lead to more weight loss.
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