Thinking of trying that trendy diet your friends raved about on Instagram? Before you’re ready to declare the latest celebrity fad the best diet plan, check the science first. While many diets promise quick weight loss, they often have a downside. We asked two USC experts to help us separate truth from hype for four popular diets that many claim to be the best diet plan. Here’s what we learned:

Diet plan: High protein, low carb

Popular diets such as Atkins and paleolithic (or “paleo”), emphasize high-protein foods throughout and low carbohydrates during their initial phases. Later on, both diets slowly add back carbohydrates. Paleo, however, eliminates grains, legumes and dairy.

The Good: Few hunger pangs since protein helps to suppress your appetite. Many rave that low-carb is the best diet plan because you’ll lose weight as the diet causes your body to enter “ketosis,” a process that shifts it from using carbs to burning fat for fuel. By removing sugars, starchy food and refined flours, it also improves your insulin levels. “The more carbs you can cut out, the better, especially sugars and highly processed foods, which tend to be higher in carbs,” said Michael Goran, co-director of the Diabetes and Obesity Research Institute at Keck School of Medicine of USC. “A high-carb diet generates a lot of glucose, which means you have to produce more insulin to clear it. This stresses your body and, over time, can contribute to cardiovascular disease or diabetes risk.”

The Bad: Cutting carbs at the most extreme level can lead to eliminating fresh fruit and vegetables, which means you miss out on their nutritional benefits. Eating a lot of protein without the fiber can lead to constipation, especially at the start. You may also feel tired and irritable during the first two weeks as your body shifts to burning fat for energy. Emphasizing meat protein leads to consuming too much saturated fat — especially when plant-based sources like beans and legumes are restricted or eliminated.

Diet plan: Ketogenic (Keto)

The ketogenic diet is a variation of Atkins that calls for extremely low carbohydrates, moderate protein and high fat.

The Good: Like Atkins, the diet lowers insulin levels and shifts your body to burning fat. It may also improve your cholesterol levels.

The Bad: When you decrease your fiber intake drastically, you’re at a higher risk for constipation. The diet also leaves you feeling grumpy for the first few weeks. “That’s because you lose the serotonin and the energy you normally get from carbohydrates,” said Claudia Del Vecchio, nutrition educator at Keck Hospital of USC. “A lot of people also go through sugar withdrawal and feel edgy. But after a few weeks, they feel better.” This is not the best diet plan for all though: it should be avoided by anyone with kidney issues, because constant ketosis changes urine chemistry and raises the risk of developing kidney stones.

Diet plan: Juice cleanses

Made up of fruit, vegetable or a combination of juices, this liquid diet reduces calories and mimics fasting. If done for more than two days, it also shifts the body into burning fat for energy.

The Good: It lowers insulin levels and allows your metabolic system to rest. “By resting the processes involved in digesting food, you reduce things like stress hormones and insulin-like growth factors, which may reduce your cancer risk,” Goran said.

The Bad: You’ll probably feel hungry. If you drink a lot of fruit juice, you may feel moody as your blood sugar surges, then drops. If a cleanse lasts more than few days, your body thinks it’s starving and shifts to burning fewer calories. Also, if you’re opting for juice instead of eating whole fruit, you’re getting a high dose of sugar but none of the fiber that can slow down absorption and make you feel fuller.

Diet plan: Raw foods

This diet typically includes raw vegetables, fruit, nuts and sprouted grains. Some versions include unpasteurized dairy, raw eggs or fish.

The Good: You’ll get plenty of fiber, vitamins and minerals by eating whole, unprocessed food.

The Bad: Because it’s so high in fiber, you may feel gassy, bloated and have frequent bowel movements. You also may get exposed to toxins found in some raw foods or miss out on nutrients that are more easily absorbed when foods are cooked. “For example, the antioxidant lycopene in tomatoes is more bioavailable when the tomatoes are heated than when eaten raw,” Del Vecchio said. “Button mushrooms contain carcinogens that get destroyed only when cooked.”

While all four diets can help you lose weight, Goran recommends the best diet plan as one for longterm good health. Stick with a balanced diet, which includes whole foods and plenty of fruits and vegetables, and cut out highly processed foods, sugar and simple carbs. For the best and healthiest way to sustain your goals, Del Vecchio recommends consulting with a nutritionist or medical provider — not Instagram — to determine guidelines that best match your lifestyle and health background.

— Koren Wetmore