But although the right diet may help you gain a svelte figure, the wrong one might be a disaster for your skin.
We asked an A team of skin experts for their opinions about some popular weight-loss regimens. They included celebrity dermatologists Jessica Wu, whose new book, "Feed Your Face," hits shelves Feb. 1; Howard Murad, author of "The Water Secret: The Cellular Breakthrough to Look and Feel 10 Years Younger"; and David Colbert, author of "The High School Reunion Diet," who also has a degree in internal medicine and has been a consultant for Chanel. We also asked dietitian Linda Illingworth, director of nutrition at the famed health spa Cal-A-Vie, to weigh in on fad dieting and share tips on achieving beautiful, glowing skin even as you work toward a slimmer, healthier body.
Super low calorie diets
The human body is designed to function on a varied diet, Murad says, and it's engineered to make the most of a broad mix of vegetables, fruits, grains, proteins and fats to obtain vitamins, antioxidants, glucosamine, essential amino acids and minerals. Fad diets or those too low in calories (roughly fewer than 1,400 a day for men and 1,000 per day for women) can deprive the body of this variety of healthful foods, thus depriving it of the raw materials for healthy new cells and critical vitamins that are essential to building and preserving collagen. This can make the skin lose elasticity and sag, "making you look much older than your real age," Murad says. Skin may become extremely dry, lackluster, sallow and prone to infection. Extreme dieting consequences also include broken nails and dull, brittle hair.
"In the long term, extreme dieters can lose their hair completely," Murad says. Very low calorie diets can be so stressful that the body goes into a starvation survival mode, "which oddly enough makes you store fat once you end your restrictions."
The master cleanse
This regimen, purportedly used by celebrities in search of quick weight loss, involves drinking a laxative tea at night, drinking salt water in the morning and then consuming nothing but a concoction of lemon juice, water, maple syrup and cayenne pepper the rest of the day.
The cleanse has many of the same problems associated with other nutrient-restricting diets. And don't be fooled into thinking that the water in liquid-based diets like this one will help your skin by itself.
True, the skin's epidermis (the outer layer of the skin) contains cells that, when plump with water, have a nice cell membrane to keep the water within the cell. The dermis (the layer below the epidermis) is made of water-absorbent collagen, elastic tissue and reticular fibers. With enough collagen in your skin, you have fewer wrinkles. But just drinking a lot of water isn't enough by itself to help, because "water can go right through you," Murad says.
"As we age and have disease, our cell membranes become thinner and thinner and become porous and lose water," Murad says. In addition to drinking water, "we need to also strengthen and repair the cell membranes to keep the water in." This process requires a varied, healthful diet.
"What is amazing is that some extreme dieters develop rashes and acne-like lesions on their skin due to the stress on their system but tell themselves that these symptoms mean that they are purging toxins," Murad says. "Your body does a fine job of purging waste and impurities without the shock of extreme dieting."
As to the saltwater flush that's part of the regimen, Murad warns that salt water can simultaneously dehydrate and cause bloating.
High protein, low carb
"Without adequate carbohydrates, the body breaks down fat for energy," Illingworth says. "This robs the skin of fatty acids necessary to maintain cell structure, moisture and softness."
She adds that the ketones produced as the body burns fat create a more acidic environment in the blood and are toxic in higher concentrations, creating inflammation of the blood vessels that feed and nourish the skin. "This is often seen in the ruddy complexion of alcoholics. Eventually the blood vessels can be seen at the surface of the skin — tiny, red and broken." Also, you may have less energy to exercise, which could deprive the skin of proper blood circulation and make it dull.
Extreme low-fat diets
"These diets make us fatter, first of all," Illingworth says. "Secondly, without adequate fat in the diet, it's very difficult for the body to get the essential fatty acids that become part of the cellular structure of the skin and arteries and make them soft, pliable and moist."
She says that for most people on this kind of diet, carbohydrate consumption increases dramatically, which can lead to higher blood sugar and increase irritation in the arteries. Over time, this irritation damages the blood vessels that bring nourishment to the skin. "Also, glucose will bind with proteins in a process called glycation, making cells stiffer, less pliable and more subject to damage and premature aging," Illingworth says. "This process is considered a rather significant aspect of aging of the skin. High blood sugar is also seen as the culprit in teenage acne … not fats, as once thought."