Diet plans ranked: Jenny Craig No. 1

What's the best diet for your weight loss investment?

According to Consumer Reports, it's Jenny Craig.

The weight loss plan received a first place ranking in a listing by the magazine.

So, does that make Jenny Craig the best plan for you?

According to CBS News Medical Correspondent Dr. Jennifer Ashton -- not necessarily.

On "The Early Show," Ashton and Nancy Metcalf, senior program editor for Consumer Reports, discussed the diet plan rankings and what they mean for you if you're ramping up to lose weight.

Metcalf explained the rankings were based on clinical studies of the diets.

She said, "We crunched the numbers on how much weight people lost in the short term, six months, in the long term, a year. How many people stayed on the diet. And then we also analyzed the nutritional content of the diet and gauged how well it went with the federal guidelines and crunched all those numbers together to get the big rating."

"Early Show" co-anchor Erica Hill noted Jenny Craig was "far and away" No. 1.

Metcalf said, "Some new studies came out last year of Jenny Craig, which had great results. After a year, the average participant had taken off eight percent of their weight, which doesn't sound like a lot, but actually is kind of a home run for a big diet study. ... And they kept it off for a year."

Ashton noted the study that Consumer Reports based their results on by the Journal of the American Medical Association was funded by Jenny Craig.

" We have to have that out there," Ashton said.

Slim Fast earned the No. 2 spot.

Hill remarked, "That seemed a little surprising to me. I thought it would be a quick fix, not a long-term fix."

Metcalf said, "It kind of is. They get good results six months level. But what you see after a year is people just drop out. Because I think maybe they get tired of eating the same stuff all the time."

Hill noted Weight Watchers took the third place spot and the Zone plan came in fourth.

Flexibility, Hill pointed out, is important for people looking to lose weight - but which plan has the most?

Metcalf recommended No. 3 finisher, Weight Watchers.

She said, "As I'm sure most people know, you get a point -- you know, you get some points, and you can really spend them anywhere you want, although the diet pushes you to eating really healthfully, a lot of lean protein, vegetables, whole grains, and that sort of thing."

Hill said, "You makes your own choices as opposed to Jenny Craig, which are prepackaged meals."

Consumer Reports diet plans ranking:

1. Jenny Craig
2. Slim Fast
3. Weight Watchers
4. Zone

But how do you pick the best diet plan for you?

Ashton said "a couple of medical caveats apply."

"No. 1 - is it safe?" she explained. "A lot of diets can affect weight loss in the short-term, but they might be dangerous to your health. In terms of caloric intake; you don't want to go below 1,200 calories a day if you're a woman, 1,600 if you're a man."

She continued, "If you're picking the diet plans, ask yourself a couple of questions. Who's managing it, nutritionists, dietitians, physicians; are there social workers involved? And what, exactly, are they promising you for what amount of money? Because we have to remember, one of the goals of the commercial diets is weight loss. The other one is making money. You want to do your due diligence."

Metcalf added people need to consider personal eating preferences.

"If you're a person who really doesn't like prepackaged foods, something like a Jenny Craig, although it has great results, might not be right for you," she said. "If you're a vegetarian, Atkins is not going to be your diet."

Hill said, "Atkins wasn't even in the top four. We heard so much about the low-carb craze. Does that not work?"

Ashton said, "The low-carb controversy continues - continues to be a controversy. There's some important medical and nutritional dietary facts you need to know about that. Not every carbohydrate is equal and not every carb is evil."

She added, "When you talk about these low-carb diets, they are effective in weight loss, and they can be safe if you're getting the healthy carbs, the whole grains, and the fruits and the vegetables, and if you're not substituting high-fat in place of those carbs that you're trying to avoid. So if you're talking about eating lean protein and a lot of fruits and vegetables and taking low-carb in conjunction with that, (it) can be very, very effective. The thinking there is that high-carbohydrate diets really stimulate our insulin production, which stimulates our appetite and gets directly deposited into fat whatever we don't use as an immediate use of energy."

As for support groups with these diets, Metcalf said it's an under-appreciated aspect of the plans.

She said, "Jenny Craig includes -- you pay for this -- but you have an either in-person or phone support every single week to really keep it in their head that they're supposed to be on the diet."

Weight Watchers, Hill noted, has meetings.

But whatever plan you choose, Ashton said the immediate benefits to weight loss are huge.

"Even about five percent of weight loss can pay off to a huge health benefit," she said. "The key long-term, it has to be sustainable. It has to work for you."