6 of the Most Interesting Things We Learned About Weight This Year

Here's a frustrating fact: More of us are trying to lose weight than ever before, but the average American BMI and weight is still increasing, according to a November 2019 study published in JAMA Network Open that tracked more than 48,000 adults for 15 years.

Despite decades spent on research and billions spent on products — the weight-loss industry is estimated to be worth $245 billion by 2022, according to an October 2019 report from market research firm Markets and Markets — it turns out we still have plenty to learn about losing and managing weight.

Sometimes the things we learn about weight are big and flashy, like in May 2016, when America's fascination with The Biggest Loser TV show came to an abrupt end. Research published in Obesity and highlighted in a major New York Times feature revealed the show's rapid, extreme weight-loss methods actually slowed the contestants' metabolisms and led to significant weight gain over the long term.

But usually findings are much more incremental. Over years — or even decades — a small, preliminary study examining a hunch grows into long-term, robust research that finally confirms a hypothesis.

Frankly, we don't usually cover those earliest stages. The last thing we want to do is mislead our readers into thinking science is further along than it actually is. But some of the most interesting and promising weight studies of 2019 also happen to be in their infancy.

To give you a sense of where the research currently is and what direction it will be going in the years to come, here are some of this year's aha! moments that shifted our thinking (or, in some cases, confirmed our suspicions) about the best ways to lose weight and keep it off for good.

The high-fat, extremely low-carb keto diet has been one of the most popular eating plans (if not the most popular) of the past 24 months, particularly for people who want to shed body fat. But an August 2019 study published in the Journal of Hepatology threw keto's effectiveness into question by suggesting that a more moderate Mediterranean diet could be the better way to go.

The 18-month experiment involved 278 people with obesity who were assigned to either a low-fat diet or a Mediterranean diet that was higher in fat and fairly low in carbs, but not as extreme as keto.

Compared to the low-fat dieters, people on the low-carb Mediterranean diet lost more visceral fat, the harmful type stored deep in your belly and around your organs. The Mediterranean dieters also saw bigger improvements in heart health than the low-fat eaters — and that's after accounting for the positive effects of fat loss.

There's lots of research on the Mediterranean diet, which focuses on eating healthy, unsaturated fats like those found in olive oil, avocados, fatty fish, nuts and seeds. In a March 2019 review published in Nutrients, researchers linked the diet to lower body mass index (BMI), lower waist circumference and weight loss, albeit at a slower (but healthy) pace than other weight-loss diets.

What's more: Unlike keto, which embraces saturated fats (found in animal-based foods like meats and cheeses), the Mediterranean diet's unsaturated fats can boost protective HDL cholesterol, lower "bad" LDL cholesterol and reduce triglycerides, dietitian Laura Burak, RD, CDN, tells LIVESTRONG.com.

"Having quality fat in your diet can actually help you stay at a healthier weight and make you feel much more satisfied," she says.

It doesn't matter if you hit the gym in the morning one day and after work on another, right? Not so fast: Exercise timing might actually be more important than previously thought, according to an August 2019 study in Obesity.

The study involved 375 weight-loss maintainers (they had all dropped 30 or more pounds and kept them off for at least a year) who got plenty of regular exercise. Most were consistent about when they worked out, whether it was morning, afternoon or evening.

No matter what time of day they worked out, the most consistent participants exercised more often and for longer periods of time, on average. They were also more likely to hit the fitness target recommended by the U.S. Department of Health and Human Services (HHS): at least 150 minutes of moderate-intensity activity per week.

Separately, a small July 2019 study published in the International Journal of Obesity found morning exercisers lost more weight, on average, than people who worked out in the evening; however, more research is necessary to determine why that might be the case, the study authors noted.

Yes, this might already sound familiar, but we're not just talking about doughnuts and potato chips. Any food that's commercially made with five or more (usually a lot more) ingredients and includes substances you wouldn't normally cook with at home (like modified starches or hydrolyzed proteins) is considered "ultra-processed," according to definitions laid out in a February 2019 report in Current Developments in Nutrition.

That means even seemingly innocent kitchen staples like breakfast cereal and fruit-flavored yogurt or frozen turkey meatballs and store-bought marinara sauce are included in this category.

Past research, including a December 2017 review in Current Obesity Reports, has tied ultra-processed foods to higher weight. But these studies have always only found a connection between the foods and weight gain — they've never shown the foods caused those added pounds.

That changed in May 2019. In a small but groundbreaking study from the National Institutes of Health and published in Cell Metabolism, 10 men and 10 women followed one of two diets for two weeks, then switched to the other diet for two weeks. One was "ultra-processed," containing ingredients like hydrogenated oils and high-fructose corn syrup, and the other was "unprocessed," featuring a variety of whole and minimally processed foods. Both diets provided similar amounts of sugar, fat, fiber and macronutrients.

Read more: 5 Health Risks of Eating Too Many Processed Foods

Even though the participants could serve themselves as much or as little as they wanted during both phases of the study, they ate more calories — about 500 more a day — while they were on the ultra-processed diet. They also gained about a pound a week, versus a loss of about the same amount when they were on the unprocessed diet.

"These are landmark findings that the processing of the foods makes a huge difference in how much a person eats," Dariush Mozaffarian, MD, MPH, dean of Tufts University's Friedman School of Nutrition Science and Policy, told NPR when the study was published.

While the study stopped short of pinpointing why the ultra-processed foods had this effect, the study's lead author noted that calorie density might have played a role: Although the two diets' meals were matched for protein, the ultra-processed meals were more calorie-dense per bite, meaning people had to consume more fat and carbs to hit their protein needs.

You've likely heard the buzz around intermittent fasting (IF), which involves alternating periods of fasting and feeding.

The specifics vary from plan to plan: You might fast every other day, or eat normally five days a week and then severely restrict calories the other two days. Another variation called time-restricted eating limits noshing to a certain window of time each day, usually during daylight hours.

"If you're restricting after-dinner meals, you have a longer fasting period, and that's going to have beneficial effects on your metabolic health," says William Kraus, MD, professor of medicine in the Division of Cardiology Medicine at Duke University School of Medicine.

Findings from several recent studies suggest that intermittent fasting can be effective for weight loss, but one of the most comprehensive was published October 2019 in the Journal of Clinical Medicine. The research linked intermittent fasting to significantly lower BMI and fat mass compared to a control diet.

Building on previous findings, a small, first-of-its-kind August 2019 study in Obesity looked at why IF might be an effective way to lose weight. Researchers examined how calorie burn changed when people ate on an earlier, time-restricted schedule of 8 a.m. to 2 p.m. versus 8 a.m. to 8 p.m.

Each of the 11 men and women in the study was assigned to one schedule for four days and then was assigned several weeks later to the other schedule for another four days. Eating earlier in the day didn't substantially affect calorie burn, researchers found, but it did lower appetite and boost fat burning, both of which can help with weight loss.

While this tiny study gives us a peek into how IF prompts weight loss, we need larger, rigorous trials that follow people for more than a year before we can make strong recommendations about IF, according to the Harvard T. H. Chan School of Public Health. Future studies should also look into any negative side effects, such as nutrient deficiencies, according to the Academy of Nutrition and Dietetics.

Studies have shown that animals live longer, healthier lives when scientists put them on a calorie-restricted diet. But what about people?

The first human trial of its kind suggests the same theory might apply. In September 2019 research published in The Lancet Diabetes & Endocrinology, Dr. Kraus led a team that placed more than 200 healthy adults into one of two groups: Participants in one group were asked to cut their calorie intake by 25 percent for two years; the others ate like they always did.

Two years later, the calorie-cutters only managed to reduce their daily intake by 12.5 percent, on average — far short of the target. Even so, that trimming (roughly 300 calories) made a difference: They maintained a 10 percent weight loss, on average, and reduced body fat.

What surprised researchers most was the way cutting 300 calories improved high blood pressure, cholesterol and other risk factors for heart disease, and that those perks occurred in younger, relatively healthy-weight people without any underlying heart issues, Dr. Kraus tells LIVESTRONG.com.

"What that means is this was not just a weight-loss study," he says. In fact, weight loss only accounted for about 25 percent of the heart-health benefits.

Rather, it's "something about restricting calories itself" that's key, Dr. Kraus says. Even in otherwise-healthy people, cutting calories (without changing the makeup of your regular diet) may be smart, he says, although researchers don't yet know exactly why that might be.

Have you heard this one before? "Only continuous, 10-minute bouts of aerobic activity 'count' toward your weekly exercise goal." That's what guideline groups used to tell Americans, but now we know that's just not true.

After reviewing all the available scientific literature published on the topic since 2008 (the last time the guidelines were updated), the U.S. Department of Health and Human Services (HHS) updated its Physical Activity Guidelines for Americans in November 2018. But it wasn't until this year that the science behind that new advice made it into major medical journals, including the June 2019 issue of Medicine & Science in Sports & Exercise.

That's when it became clear that moderate-to-vigorous physical movement of any duration — not just formal exercises performed for at least 10 minutes — counts toward your daily aerobic activity quota; even if you're just climbing a few flights of stairs for a few minutes, according to the American College of Sports Medicine (ACSM). And all of it is good for your health.

The old "calories in, calories out" adage is just one small part of the weight-loss equation. And while 2019 was an informative year in weight-loss research, we still need future studies to shore up the most interesting new findings. In the meantime, if you're looking to lose weight in 2020, we've pulled together a collection of science-backed weight-loss and management methods that are much better for your body and mind than dieting.