Jan. 4, 2016 -- So you’re finally ready to lose weight. Now the question is: How?

The standard advice -- to eat less and move more -- isn’t so helpful when it comes to the “how.” You probably know you need to cut calories, but how many? Are you better off getting those calories from low-fat or low-carb foods? And what’s going on with your metabolism, your personal energy-burning furnace? Is it programmed to keep you overweight? Is there any way to fan the flames so you can dream of one day eating a piece of pie without gaining a pound?

Even science is still stumped on many of the basic questions of weight loss.

“Amazingly, in this era of obesity, there are still many things that we really don’t know,” says Robin Callister, PhD, professor of human physiology at the University of Newcastle in Australia.

Here’s what we do know about some of the most persistent mysteries of weight loss.

The idea that dieters need to cut this many calories -- with diet, exercise or both -- to lose 1 pound of weight comes from an influential scientific paper published in 1958. Max Wishnofsky, MD, a doctor who lived in Brooklyn, N.Y., tried to sum up everything we knew about how calories are stored by the body. He concluded that when the body is in a steady caloric state -- meaning it isn’t fasting or starving -- extra calories will be stored as fat, and it would take 3,500 extra calories to create a pound of fat. In that same steady state, he also said it would take a deficit of 3,500 calories to lose a pound of weight. For decades, the “Wishnofsky Rule” has been math that determined dieters live by.

The trouble is that it’s wrong.

The 3,500-calorie rule doesn’t work because the body adjusts to weight loss. It quickly decreases the number of calories it needs to maintain its new, lighter size, says Corby Martin, PhD, director of the Ingestive Behavior Laboratory at the Pennington Biomedical Research Center in Baton Rouge, LA. That means weight loss slows down over time. People who expect to drop a pound for every 3,500 calories they cut will soon become frustrated when the scale doesn’t cooperate.

Let’s say a dieter knows they need to eat 2,500 calories a day to maintain their current weight. But they want to slim down. So they decide to shave 500 calories off their daily intake. According to the Wishnofsky Rule, after about a week of doing that, they should lose a pound.

“For the first week or two, the 3,500 calorie-per-pound rule kind of works, roughly, but after the first couple of weeks it doesn’t work,” Martin says.

Here’s why: In 3 or 4 weeks, you need less food to maintain that new, svelter shape.

The good news is that researchers have been working hard to update Wishnofsky’s formula. There are new calculators, like the Body Weight Planner available from the NIH and the Weight Loss Predictor from Pennington. Give them a few key details, like your sex, age, weight, height, activity level, and the date you want to hit your goal, and they’ll give you a more realistic daily calorie goal to get you there.

Once you know how many calories you need to eat every day, where should they come from? Is it better to cut carbs or cut fat? How much protein do you need each day? Will having a drink torpedo all your hard work?

Let’s start with the alcohol.

“There’s a big debate on whether alcohol calories are even useable, whether you can even turn them into fat. It’s not easy,” says Ken Fujioka, MD, a weight loss expert at Scripps Health in San Diego, CA. “When you look at various studies you actually get mixed results. Some studies say it’s not a problem, don’t worry about it, others say it’s associated with weight gain. So it’s a real open mess.”

Fujioka counsels his patients to pay attention to how alcohol affects their eating.

“Some folks, when they drink alcohol, feel like they have license to eat whatever they want to, and they get into problems,” he says.

If a glass of wine weakens your will to resist that plate of cheese and crackers, it’s not doing your waistline any favors.

But if booze doesn’t affect your eating, then one or two drinks is probably OK, he says.

As for calories from fat, carbohydrates, and protein, this is where one size, or one eating plan, really doesn’t fit all.

There is good science to show that people who have high blood sugar levels -- associated with conditions like type 2 diabetes, prediabetes, gestational diabetes, polycystic ovary syndrome, and fatty liver disease -- benefit from diets that are lower in refined carbohydrates and higher in healthy fats and lean proteins. Examples of this kind of diet are South Beach, the Zone diet, the Mediterranean diet, and the low GI diet.

If insulin levels aren’t a concern, there’s little difference in the amount of weight people lose if they cut their calories from fat or from carbs, says Kevin Hall, PhD, a senior investigator and expert in metabolism at the National Institute of Diabetes and Digestive and Kidney Diseases in Bethesda, MD. But he says protein calories are a different story.

In the lab, researchers have shown that higher-protein diets tend to increase the number of calories a person burns, Hall says. “So in that sense, a protein calorie is not equivalent to a carbohydrate or a fat calorie,” he says.

Protein helps you burn more calories during the day and helps preserve muscle. When people lose weight, they don’t just lose fat -- they also lose muscle. The more muscle you lose on a diet, the more your metabolism slows. That can make it tough to keep the weight off down the road. Protein also helps you feel satisfied for longer after your eat.

But people can eat only so much protein without changing their kidney function. U.S. dietary guidelines recommend that adults keep their protein in a range of 10% to 35% of total calories each day. Most diets fall into that range. Atkins, for example, one of the highest-protein diets around, supplies 35% of daily calories from protein.

To a large extent, yes, you were.

Genes are “at least 40% of the answer,” Fujioka says, and they may explain as much as 80% of our weight.

He says that’s especially likely to be true if a person is very overweight or obese and has struggled with being heavy their whole life.

“The potential to gain weight and become obese is in everybody. But for some people, the potential is clearly genetically much, much higher,” he says.

So far, more than 30 genes have been flagged as being linked to body mass index. The one most strongly tied to obesity is called the FTO gene. Researchers recently reported that people who get a faulty copy of that gene are more likely to store calories as fat instead of burn them for energy. The discovery, which was published in the New England Journal of Medicine, should pave the way for better weight loss treatments.

Though FTO is the most powerful single gene found to date, it doesn’t explain all obesity. Fujioka says obesity is probably the sum of many genes working together.

“The more genetic flaws you get that lead you to obesity, you’re more like a loaded gun. The environment will pull the trigger and you’ll just get heavy.”

Whereas people who don’t inherit those risk genes will be protected, to some extent, from weight gain, no matter how badly they eat.

If losing weight with your mate has you discouraged, ladies, take heart.

Yes, it’s true -- pound for pound, a man on a diet will drop 10 pounds faster than you can say “please pass the celery.” And researchers think that’s probably more of a size problem than a sex difference. Men are bigger than women and naturally carry more muscle, the tissue that burns the greatest number of calories. So they do have an easier time losing weight.

But here’s the thing about men: They start strong, but they often can’t sustain the effort.

“At 3 months, men are ahead -- definitely ahead on absolute weight loss,” says Callister, who recently conducted a study of studies, or meta-analysis, to look at the big picture of sex differences in weight loss. “But by 6 months, there’s no difference,” she says.

But do men really lose a bigger percent of their overall weight when they diet than women do?

Surprisingly, few studies have looked at that question. Callister says we still don’t know the answer.

One interesting study, though, compared the weight loss between men and women who had gastric bypass weight-loss surgery. The study found that after 24 months, there was no significant difference in the percent of weight lost by men or women after bariatric surgery. On average, men had lost about 66% of their excess weight, while women had lost about 73% of their extra pounds.

And here’s more heartening news: While women may take a little longer to shed the same weight as men, Callister says they seem to do a better job keeping it off, perhaps because they lost it more gradually in the first place.

When it comes to dropping pounds, there’s no substitute for pushing back from your plate. But what about exercise?

While it’s important for overall health and mental well-being, it’s probably not going to help you dramatically shrink your size.

“It has dozens and dozens of benefits, but when it comes to producing clinically meaningful weight loss -- weight loss of 5% to 10% or more -- you really want to focus on dieting,” Martin says.

Exercising when you’re trying to lose weight is tricky. It does help burn calories, but not nearly as many as not eating those calories in the first place. And exercise increases appetite, so if you’re working out intensely, it’s really easy to eat back all the calories you just burned.

Martin recommends that people who are trying to lose weight focus on moderate-intensity physical activities, like brisk walking or gardening.

The National Weight Control Registry, which tracks people who’ve successfully lost 30 pounds and kept it off for a year or longer, reports that 94% of members have increased their physical activity in some way. The most frequently reported form of exercise is walking.

Where exercise becomes critically important is for weight maintenance. Martin says most people who successfully lose weight and keep it off exercise a lot -- nearly an hour a day.

Show Sources


Robin Callister, PhD, professor of human physiology, University of Newcastle in New South Wales, Australia.

Corby Martin, PhD, director of the Ingestive Behavior Laboratory, Pennington Biomedical Research Center, Baton Rouge, LA.

Kevin Hall, PhD, senior investigator,  National Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD.

Ken Fujioka, MD, endocrinologist, weight loss expert, Scripps Health, San Diego, CA.

New England Journal of Medicine, Sept. 9, 2015.

European Journal of Internal Medicine, December 2014.

Obesity Reviews, February 2015.

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