Right now, a lot of Americans are getting their skis out of the attic and trying to fit into last year’s snow pants. More than a few will regret drinking that extra cup of eggnog.

To mark the season, consumer DNA testing company 23andMe is kicking off what it terms a “massive study” into the genetic basis of weight loss that it says will ultimately involve 100,000 people.

The company, based in Mountain View, California, says that starting this week it will begin contacting 1.3 million of its customers with an offer to take part in the project by sticking to one of two diets or an exercise plan for three months, reporting back on whether their waistlines grew or shrank.

The crowdsourced study may prove to be the most comprehensive attempt yet to discern the links between people’s genes and dieting success. 23andMe hopes what it learns will let it create predictive models that provide tailored weight loss advice as part of its consumer genetic reports.

Already, consumers can pick from a dozen or more DNA tests that promise diet insights. But the tests have come under withering criticism from prominent doctors who say they’re no better than the tips you’d get from a nutritionist or a friend at the gym. The advice might be okay; it’s the DNA test that’s a waste of money.

According to 23andMe, previous studies attempting to link DNA to dieting outcomes haven’t had enough participants to zero in on genetic factors. Its new project will involve 10 to 50 times as many volunteers as previous work, says Geoffrey Benton, the company’s head of health R&D.

The company holds DNA data on more than three million customers who have sent in saliva samples. That makes it one of the two or three largest biobanks in the world. After customers’ DNA is analyzed, they receive reports about their geographic ancestry, how many Neanderthal genes they have, and a few hereditary health risks.

Buyers also receive a prediction of their body mass based on their genes, a report telling them whether they have an inborn tendency to be heavier or thinner. The problem is 23andMe can’t yet tell them what to do about it, making the results mostly irrelevant.

23andMe has always sent its customers health surveys to fill out. But starting last May, it began exploring whether it could also convince them to carry out at-home experiments. It began with a pain tolerance test in which it asked customers to see how long they could keep a hand in a bowl of ice water.

That was followed by a sleep study in which about 6,000 volunteers were randomly assigned to change their behavior in specific ways, like avoiding coffee or agreeing not to look at a screen starting 30 minutes before bedtime.

“We wanted to see if we could actually do an interventional trial from start to finish and do it remotely from 23andMe,” Benton says.

With the new dieting study, 23andMe will randomly assign people to one of three plans. Some will avoid bread, cakes, and other carbohydrates. Another group eat more fiber but will shun animal fat. A third will eat as usual but add workouts to their week. They’ll report back to the company about how often they have “cravings,” whether they’re stressed, and if they succeed in following the diets.

The company thinks that people, on average, will have roughly the same results on all the plans. What it may be able to figure out, though, is whether there are genetic or personal reasons why some individuals will end up losing 40 pounds, and others gaining 10, no matter which advice they follow.

With its diet study, 23andMe could end up demonstrating that its “platform” is suited to carrying out very large clinical trials of the type normally performed by research universities or drug companies. That could be commercially valuable, since 23andMe already sells genetic data to pharmaceutical companies and sometimes helps them locate people with specific diseases, like lupus.

For now, 23andMe still operates within definite limits. Its customers are self-selecting and not necessarily those with the serious diseases scientists most want to look at. As a result, its studies typically involve common conditions like insomnia, depression, or in this case, obesity. About 37 percent of American adults are obese, according to government tallies.