“A lot of people think the foundation of a paleo diet is high-fat meat, but I suggest that it’s vegetables,” says Hultin. The concept is to eat only foods — including meat, fish, poultry, eggs, fruits, and vegetables — that would have been available to our Paleolithic ancestors. This means grains, dairy, legumes, added sugar, and salt are all no-no’s.
The researchers hypothesize that participants who abstained from animal products dropped significantly more pounds since plant-based foods include loads of filling fiber and slow-to-digest complex carbs. Though more research is needed to confirm these results, the study authors write, "Vegetarian diets appeared to have significant benefits on weight reduction compared to non-vegetarian diets."
Make sure that the diet has been studied extensively for safety — and discuss any changes with your physician or registered dietitian before beginning a new diet. (If you don’t have a dietitian, find one in your area at the Academy of Nutrition and Dietetics website.) And do a self-check to ensure the diet fits with your own values and preferences.
Consequently, researchers have widely discredited the hCG diet, which involves using hCG injections, pellets, sprays, or drops, and consuming  as few as 500 calories daily. The diet is problematic not only because there’s a lack of research on hCG supplements, but also because the calorie requirement is dangerously low, potentially leading to nutrient deficiencies, fatigue, hormone imbalances, blood clots, and other issues. Thus, most experts agree the hCG diet is not safe for anyone, the Mayo Clinic notes. (35)
If you want to lose weight fast, your best bet is the HMR Program, according to the health experts who rated the diets below for U.S. News. While these diets enable quick weight loss for those with a short-term goal – there's a strong chance you'll drop significant weight within the first 12 months – keep in mind that this is markedly different from long-term weight loss, which is more important for your health.

Real talk: It could take weeks or months to see the metabolic effects of exercise on the scale, and even then, building muscle, which is denser than body fat, could lead to weight gain. "Do what you like because it’s good for you," Dr. Seltzer says, noting the way exercise is awesome for your heart, mental health, and more—and that not all measure of progress can be seen on the scale.
Right now, 2 out of 3 Americans are overweight or obese, and the number keeps skyrocketing year after year. Some experts consider obesity an epidemic more dangerous than that of opioids due to its role in the rise of life-threatening conditions such as diabetes, stroke, certain cancers, asthma, and osteoarthritis. Obesity is responsible for 18% of deaths among Americans over 40 years old, and 1 in 5 children in the US suffers from obesity. The medical costs for obesity-related treatments have now reached an exorbitant $150 billion per year.
The best diet for losing weight is Weight Watchers, according to the experts who rated the diets below for U.S. News. Volumetrics came in second, and the Flexitarian Diet, Jenny Craig and the vegan diet were third on this overall weight loss ranking list, which takes into account short-term and long-term weight loss scores. Some other diets performed as well or better in our rankings for enabling fast weight loss, but long-term weight loss is more important for your health.
Rather than rely entirely on the information provided by the companies to determine weight management effectiveness, we spent weeks browsing through hundreds of unpaid customer testimonies (not endorsed by any company) to get a feeling on the accuracy of the claims they make. In fact, these testimonials provided us with a much more truthful and in-depth insight regarding how effective diet plans really are. 
Forget old low-carb diet plans that focused on processed protein bars and shakes. This year, the keto diet got high marks for low carb. Keto, short for "ketogenic," is all about training the body to burn fat for fuel. How? By eating fat—and lots of it. Most keto diets recommend getting at least 70 percent of your daily calories from fat and the rest from protein. The goal is to eat as few carbohydrates as possible. Proponents say it helps them drop weight fast with little or no hunger in addition to perks like more energy and mental clarity. (Interested? Here's everything you need to know about the keto diet.)
If you have more than a week to lose 10 pounds, Dr. Huether recommends trying intermittent fasting. "For longer-term weight loss and maintenance, I like to use intermittent fasting where I choose an 8-hour window to eat (for me its 1 pm to 9 pm). By doing this your body learns to use fat as fuel (instead of glucose), so it becomes easier and sustainable over time."
There’s a reason everyone harps on about protein: Not only does it help keep you full, but it’s also responsible for repairing the tiny tears caused by strength training in your muscles. This helps them grow bigger and stronger, nudging out body fat in the process. As a general rule of thumb, aim to get at least 70 grams of protein throughout the day, says Dr. Cheskin.
If you like eating meat and want to lose weight, you might be tempted to try this recent extreme diet fad that proponents have made some pretty outrageous claims about. One: that eating nothing but meat can cure you of autoimmune diseases. The problem is that there’s no good research to support that notion, or any other health claim, for that matter. Indeed, omitting foods known to be good for you — fruits and veggies among them — can lead to a bunch of unwanted side effects, including constipation and potentially dangerous nutrient deficiencies. Still, since you’re cutting out so many food groups, there’s a decent chance you’ll lose weight, experts say. Regardless of any possible benefits you might see, this restrictive approach is definitely one you’ll want to ask your doc about before you even consider diving in.
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