Over the past decade, studies have pitted low-fat diets against low-carb diets to determine which one is superior for losing weight. Most have turned up similar results: There is little, if any, difference between the two diets in the number of pounds lost after a year.
Within the two diet groups, however, studies have found huge variability in weight loss between individuals, with some people losing as much as 55 pounds and others gaining up to 10 pounds.
Such variable results among people following the exact same diet has led to the idea that there isn't a one-size-fits-all weight-loss diet. Instead, certain diets may work better than others for some people based on their genetic makeup or metabolic differences.
A study published in the Journal of the American Medical Association throws water on the notion that a diet matched for your genes, or metabolic profile, will enhance your ability to lose weight.
What's more, the new findings suggest that you'll do quite well at losing weight if you focus on the quality of the foods you eat, rather than how much you eat.
For the study, a randomised controlled trial, researchers from Stanford University School of Medicine in California assigned 609 overweight adults to follow either a healthy low-fat diet or a healthy low-carbohydrate diet. Participants were not advised to cut calories; they were told to eat as much food as they needed so they didn't feel hungry.
Participants were instructed to emphasise nutrient-rich, whole and minimally processed foods, mostly prepared at home, maximise vegetable intake and to limit intake of refined flours and added sugars. They were also encouraged to follow physical activity guidelines (e.g., 150 minutes a week of moderate-intensity aerobic exercise).
People eating the healthy low-fat diet were told to eat high-quality, low-glycemic carbohydrate foods such as beans, lentils, oats, brown rice, sweet potato and fresh fruit. Low-carb followers were counselled to choose high-quality fats such as avocado, nuts, seeds, oily fish and olive oil.
Not unlike previous findings, the low-carb and low-fat diet groups lost similar amounts of weight, an average of 12 pounds after one year. And both groups experienced a wide range of weight change, from losing 14 pounds to gaining almost five.
What's unique about this study, though, is that calories weren't counted and food wasn't measured. Instead, the focus was placed on eating high-quality foods, which turned out to be a successful strategy for weight loss regardless of the diet they followed.
But that doesn't mean that calories don't matter. They do.
By eating lots of vegetables and limiting highly processed foods, participants in both groups ended up eating 500 fewer calories a day without realising it.
After looking at a number of genes shown in previous studies to influence fat or carbohydrate metabolism, the findings revealed that having a certain genotype didn't influence weight loss.
The researchers also looked at insulin resistance, a condition in which cells don't respond to the blood-sugar-clearing hormone insulin. As a result, the body tries to lower blood sugar by producing more insulin.
Past research has found that people who are insulin resistant lose more weight on a low-carbohydrate diet.
In this study, however, people who had high levels of insulin in their bloodstream didn't do better on a low-carbohydrate diet.
When emphasis was placed on choosing high-quality foods for both low-carb and low-fat eating plans, a diet based on genetic makeup or insulin resistance didn't make a difference.
The study does have some limitations. Researchers relied on participants to accurately remember what they ate and how much they exercised, which can be prone to error.
It's also possible that other genes, ones that were not assessed in this study, are significant for weight-loss response to a particular diet.
And what the study can't determine is whether participants are able to sustain their new-found healthy-eating habits.
Even so, the findings strongly suggest that eating a diet packed with nutritious whole foods results in weight loss, regardless of the proportion of calories from carbohydrates or fat.
Four ways to boost the quality of your diet:
Eliminating highly processed foods from your diet may help you lose excess weight, not to mention guard against heart disease, diabetes, certain cancers and other chronic diseases.
Eat vegetables at every meal. Add red pepper, mushrooms and baby greens to omelettes, blend kale or spinach into smoothies, pack raw vegetables or green salad with brown-bag lunches and add frozen or fresh chopped vegetables to chili, stew, soups and casseroles.
Replace white with whole grain and low glycemic carbs. Buy breads and breakfast cereals that contain only whole grains. Swap white rice and white potatoes with quinoa, farro, brown or black rice, millet, sorghum, whole-grain pasta, sweet potato or beans/lentils.
Snack wisely. Instead of granola bars, refined crackers and pretzels, snack on fresh fruit, nuts and seeds, yogurt, popcorn or raw vegetables with guacamole or hummus.
Cut added sugars. Avoid sugar-sweetened beverages (e.g., pop, iced tea, energy drinks, fruit drinks). Limit sugary treats to once or twice a week. Switch to plain, unflavoured yogurt and sweeten it naturally with fruit.