- Researchers wanted to see if people’s DNA or insulin sensitivity affected their ability to lose weight while following a low- or high-carb diet.
- Everyone lost the same amount of weight regardless of their DNA, insulin sensitivity, or whether they followed a low- or high-carb diet.
- Although the idea of picking a diet based on your genetic makeup or insulin sensitivity sounds scientific, this study shows you’re better off choosing a diet you can stick to.
DNA-based diets have been getting lots of attention.
The idea is that you send a saliva sample to a testing company which allows them to analyze your DNA. They look for a collection of variations (genes) in your DNA that are supposedly linked to certain dietary needs.
Based on the results, they tell you what foods you should or shouldn’t eat to lose weight.
According to these companies, as long as you eat foods that are compatible with your unique DNA profile (genotype), then you should be able to lose weight with ease.
Eat foods that aren’t compatible with your DNA profile, though, and you’re always going to struggle to get the body you want.
Is any of that true, though?
That’s what a team of scientists at Stanford University Medical School wanted to find out in a recent study.
Let’s see what they did.
What Did the Researchers Do?
The researchers divided 609 young and middle-aged obese men and women into two groups:
- One group followed a high-carb, low-fat diet.
- One group followed a low-carb, high-fat diet.
Although there are plenty of other weight loss diets they could have tested, low-carb diets are often recommended by these genetic testing companies.
Everyone was coached to eat plenty of whole, nutritious foods, and minimize their intake of sugar, trans fats, and other processed foods. They were also instructed on how to set up their diets in a way that would keep them in a calorie deficit throughout the study.
For the first two months of the study, everyone was told to consume no more than 20 grams of fat or carbs (depending on their group). After two months, the participants were allowed to increase their carb or fat intake gradually over the next few months so they could maintain the diet for a whole year.
This study wasn’t just about low-carb versus high-carb diets, though.
The two main questions the researchers wanted to answer were:
- Can you predict the best weight loss diet for people based on their DNA?
- Can you predict the best weight loss diet for people based on their insulin sensitivity?
There are several genes that scientists think may influence how effectively people can lose weight while following different diets.
Specifically, there are a handful of genes that researchers think may make some people more efficient at processing carbs, and others more efficient at processing fat.
So, the researchers did genetic testing on everyone in the study. Then, they recorded whether people fell into the “high-carb,” “low-carb,” or “neutral” genotype based on their results.
The researchers also measured everyone’s insulin sensitivity, which is partly determined by your DNA.
Insulin is a hormone that’s released into the blood after a meal, and its job is to “tell” cells to open up and absorb carbs and other nutrients.
If you’re insulin sensitive, that means your cells respond effectively to insulin, and your body doesn’t need to produce as much to get the job done. Having a high insulin sensitivity is a sign that your metabolism is working well.
It’s often claimed that people who are more insulin sensitive can lose weight while eating a high-carb diet, whereas people who are less insulin sensitive will lose more weight if they follow a low-carb diet.
To measure people’s insulin sensitivity, the researchers gave everyone an oral glucose tolerance test.
This involves chugging a drink that contains 75 grams of glucose (sugar), and seeing how much insulin released into the bloodstream 30 minutes later.
If less insulin is released, then you’re considered more insulin sensitive. If more is released, then you’re considered less insulin sensitive.
Based on the results of this test, the researchers categorized everyone as either a low-, moderate-, or high-insulin secretor.
Finally, the researchers made sure that people from every DNA- and insulin sensitivity based group were assigned to both the low- and the high-carb diet groups.
What Were the Study Results?
Genetics and insulin sensitivity didn’t make any difference in how much fat people lost while following either a high- or low-carb diet. Both groups lost 12 to 13 pounds over the course of the year.
The main result is that both the high- and low-carb groups lost almost the exact same amount of weight after 12 months of dieting.
Here’s what the results look like:
As you can see, the weight loss results were more or less identical.
Both groups also had their share of diet successes and failures, with some people losing as many as 66 pounds and others gaining 22 pounds after a year.
Adherence to the diets was good, too. On average, people in the low-carb group were only eating 130 grams of carbs and people in the low-fat group were only eating about 60 grams of fat per day.
Here’s the most important result, though:
People’s genetic makeup and insulin sensitivity made zero difference in how much weight they lost.
In other words …
People who theoretically shouldn’t have been able to process large amounts of carbs lost just as much weight following a high-carb diet as they did following a low-carb diet.
And, people who theoretically shouldn’t have been able to process large amounts of fat lost just as much weight following a low-carb diet as they did following a high-carb diet.
That might sound surprising, but most other studies have found the same thing.
Which diet works better almost always comes down to personal preference.
As long as people pick a diet they enjoy and that allows them to consume fewer calories than they expend, they’ll lose weight regardless of where those calories come from.
And that was the case in this study, too.
The people who lost the most weight were the best at maintaining a calorie deficit, and the people who didn’t lose weight or even gained weight ate too many calories.
To be fair, the researchers only looked at three genes in this study. It’s possible that other genes or biological factors might be better guides as to what diet people should follow for weight loss, but there’s very little evidence that’s the case.
You could also argue that the results might have been different if the people in the low-carb group had followed a strict ketogenic diet, and kept their carb intake at less than 50 grams per day. Also unlikely, though.
The researchers took a variety of other tests, including …
… and found that both groups experienced a similar decrease in every measurement, with no differences between either group.
The one difference between the groups had to do with blood lipids.
- The low-carb group had a larger rise in LDL (“bad”) and HDL (“good”) cholesterol than the high-carb group.
- The low-carb group also had a larger drop in triglycerides, which is sign of better cardiovascular health.
That said, the differences were too small to make any difference in terms of health or disease risk.
The bottom line is that whether or not you lose weight depends on how well you can stick to your diet—not on your DNA.
What Does This Mean for You?
This study adds more evidence to rule number one of dieting:
Pick a diet you can stick to.
Although the idea of picking a diet based on your genetic makeup or insulin sensitivity sounds scientific, there’s very little evidence it’ll help you lose more weight.
On the other hand, there’s a mountain of evidence that the most important factor that determines whether or not you lose weight is whether or not you can maintain a calorie deficit.
Once you understand that, what diet you choose mostly depends on which one you can stick to.
The best thing you can do to lose weight is this:
- Figure out how many calories per day you need to lose weight. (Not sure how? Read this.)
- Figure out how many calories you should get from protein, fat, and carbs every day. Not sure how? Read this.)
- Create a meal plan made of your favorite foods that provides you with the right number of calories and the right amount of protein, fat, and carbs.
Not sure how? Then you want to read this article: