It seems there is always a new and popular fad diet promising a quick fix for slimming down, but the question is, do these diets work?

Pop star Katy Perry is just one of a long list of celebrities to attribute her figure to a specific diet. In her case, it's the M-Plan, or mushroom diet.

The M-Plan is one of the latest food fads and has followers replacing two main meals a day with a mushroom based dish.

“The M-Diet claims to keep your more curvy bust area and reducing weight in your thighs, buttocks, hips, things like that,” says dietitian Angela Dufour.

Dufour says the promise of spot reduction is one of the biggest myths surrounding the M-Diet and many other fads.

She says there are many benefits to eating mushrooms, but they shouldn't be your main source of nutrition.

Dufour says this mushroom meal plan is basically another take on a low calorie diet.

“If you're replacing maybe a higher fat meat item, such as a burger, with maybe a Portobello mushroom burger, you would obviously be reducing the overall calories and fat.

Another popular fad with celebrities is the Clay Diet. Dufour warns those eager to hop on a trend to proceed with caution.

“Bentonite clay, which is the one they are talking about adding to water and ingesting it or drinking it, can be laden with arsenic and lead,” says Dufour.

The clay is said to pool toxins and metals from the body, but Dufour says the detox can go too far.

“If it's going to start pooling good metals like calcium and iron, potentially not a very good thing in terms of balancing,” says Dufour.

Many people choose to follow other detox plans such as a juice cleanse, but Dufour says we don't really need a specific diet to help our bodies detox.

“Our kidneys and our liver, that's what they're supposed to do. So in healthy individuals, we've pretty much got that covered.”

Dietitian Nicole Marchand says detox diets can be useful as a short-term way to get back on a healthy eating path, but they are not a long-term fix.

“Fad diets are pretty unsustainable, which is another reason I suppose they're called fads, something that's around for a short period of time but then fades away,” says Marchand.

Diets that eliminate large food groups can lead to nutritional deficiencies. Marchand says to avoid this practice, unless you absolutely have to.

“All of the isolated diets, whether it be the grapefruit diet, or the soup diet, or the mushroom diet, they're just not sustainable and you will need to add other components into your diet to feel healthy and to feel well.”

Marchand also says after finishing a fad diet, many people regain the weight they've lost.

“You're more likely to find the results you're looking for over time, using a healthy well balanced diet,” says Marchand.