The equation for losing weight seems simple for many -- eat less and exercise more -- but for millions of Americans, it's still a struggle.
"My metabolism has slowed down as I've gotten older," said Robert Pilot. "It's harder to lose weight."
"I realize I'm getting a little heavier around what they call the muffin-top area," said Stephanie Farmer. "I realize I have to exercise and watch what I eat."
Sonia Angel, a dietician with Memorial Healthcare in Hollywood, Florida, weighed in on two diets that advocate cutting calories two days a week.
"The Fast Diet," written by medical journalist Dr. Michael Mosley, allows followers to eat whatever they want for five days a week, but only 500 calories for women and 600 for men on the other two days.
"For example, lean protein, fruits, and vegetables," said Angel. "You're not allowed to eat 500 calories worth of chocolate bars. That's not going to work."
Angel said drastically cutting calories for two days can be harmful, especially for teenage girls, pregnant women, or diabetics.
"They can really pass out or faint or lose consciousness if their blood sugar gets low with that amount of calories," she said. "They may not be able to live on one day on that."
Angel said allowing followers to eat anything they want on the other five days may not promote the long-term change needed to maintain a health weight.
"You can do this diet for a few months and lose weight, but what are you going to do after that?" she said.
"The Two-Day Diet," by Dr. Michelle Harvie, involves back-to-back days of low-carbohydrate, high-protein eating followed by a Mediterranean diet the other five days a week.
"You're choosing whole grains, lots of fruits and vegetables, nuts, and lean protein," said Angel.
While there is no calorie counting, the diet is intended to cut normal caloric intake in half on those two days while encouraging exercise at the same time.
"It can help somebody kick start a weight-loss program and also it can motivate you to eat healthy the other days," said Angel.
Studies have shown intermittent dieting is more effective and easier to follow than continuous dieting.