Kevin Kopjak doesn’t care much about carbs, fat, sodium or high fructose corn syrup.

He generally reads only two things on a nutrition label: the portion size and the calories. He says the strategy has helped him lose and keep off 100 pounds.

“Counting calories seems to work for me,” says Kopjak, 29, of San Francisco, Calif., who did Atkins and several other diets before switching to counting calories. “But it’s a lot of discipline. When I first started, I had an Excel log, where I literally wrote everything I ate down.”

Calorie counting — one of the oldest methods of weight loss — appears to be making a strong comeback: there are new books touting the benefits of calorie restriction, calorie counting Web sites, portable calorie readers, 100-calorie snack packs.

New York City recently enacted a regulation requiring some chain restaurants to post calories on their menus, and lawmakers in California and King County, Wash., have considered similar measures.

It all makes low carb, high protein and no sugar diets seem out of fashion.

“We count in America everything but calories,” says Madelyn Fernstrom, founder and director of the University of Pittsburgh Medical Center Weight Management Center. But “calories are the single most important thing to count when you are trying to lose weight or maintain weight. There’s no way around this.”

Research backs this up. A U.S. Department of Agriculture-Tufts University study published last year revealed that when it comes to losing weight, calories count more than food types.

And most people know: take in too many calories, gain weight. To lose weight, slash calories — 3,500 calories equal one pound — through a combination of diet and exercise.

“But how do you reduce calories without having people suffer?” says Dr. Melina Jampolis, author of The Busy Person’s Guide to Permanent Weight Loss, a book that provides simple diet and exercise strategies. “It’s easier said than done.”

The USDA recommends that women ages 19 and up consume between 1,600 and 2,400 calories depending on age, height and activity level to maintain weight. For men, the numbers are 2,000 to 3,000 calories. Dietitians suggest dieters aim to lose 1-2 pounds a week, which means burning or cutting 500 to 1,000 calories more a day.

But when something as simple as a piece of coffee cake at Starbucks contains 430 of those calories, making good choices can be laborious.

Even with careful calorie counting, many registered dietitians point out that losing weight in a healthy fashion can be complex. Different people respond to different approaches.

Dieters who try to lose weight by cutting something other than calories may succeed — but that may be because cutting calories is a byproduct of their method, she says. For example, fat has 9 calories per gram compared with carbs and protein, which each have 4 calories per gram, so reducing fat will mean people are cutting calories.

Counting calories can also have its own problems, because science aside, people are people, says registered dietitian Heather Bauer, co-author of The Wall Street Diet.

“If you start to count calories, it becomes monotonous and time consuming,” she says.

She says a food diary can help people spot eating patterns but her advice to her clients is to eat less and make healthier choices.

Gillian Hood-Gabrielson, a fitness and intuitive eating coach, agrees, adding that restricting calories can lead to overeating, resulting in feelings of guilt.

She points out that most of her clients at the Chico, Calif-based Healthier Outcomes are “walking calories guides,” and are still overweight.

Her approach focuses on helping people learn to eat when they are hungry and stop when they are full. Most of her clients are emotional eaters and she works with them to give up the diet mentality.