Put the word “fast” in front of anything and it becomes infinitely more appealing. That rings doubly true when you put the word “fast” before anything linked to weight loss—especially metabolism.
The Fast Metabolism Diet isn’t technically new—it was first published in 2013 by Haylie Pomroy, who holds a bachelor of science degree in animal science from Colorado State University. (She is not a registered dietitian.) But it gained some popularity this summer after Angela Basset, at age 60, credited the diet for keeping her fit.
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So, what is The Fast Metabolism Diet, exactly?
In a nutshell, The Fast Metabolism Diet is a 28-day plan that cycles through three multi-day phases each week and claims to help rev your metabolism through macronutrient cycling—rotating periods of high-protein, high-carb, and high-fat eating within each week.
The diet restricts corn, dairy, soy, refined sugar, caffeine, alcohol, dried fruit, fruit juice, wheat (except sprouted or natural yeast wheat), and nitrates (found in processed meats) for all 28 days.
You’re instructed to eat five times per day—within 30 minutes of waking, and every three to four hours while awake. And you need to drink at least half of your bodyweight in ounces of water every day—so a 120-pound woman would need to drink 60 ounces of water. There are also supplements available for purchase for “maximum metabolism impact,” which can be taken during the 28 days and after.
Beyond that, there are three separate phases you cycle through each week. The idea is that each phase focuses on different macronutrients.
Portion sizes vary depending on how much weight you need to lose, but the other recommendations are the same for everyone. Here’s what each week looks like:
Phase 1 (days 1 & 2): high-carb, moderate protein, no fat
In this phase, which promises to help “unwind stress,” you’ll eat lots of complex carbs (like beans and whole grains) and high-glycemic fruits (a.k.a high sugar fruits like bananas and pineapples).
You’ll also eat a moderate amount of protein, but no fats, she adds.
If you want to exercise, cardio is recommended in phase one, since your body is getting lots of easily accessible energy from these high-glycemic carbs.
Phase 2 (days 3-4): low-carb, high-protein, low-fat
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The second phase claims to “unlock stored fat” by cutting carbs and adding more protein to your diet, along with lots of green vegetables says Pomroy.
She says the extra veggies help balance out the meat consumption, and this state of balance helps improve the body’s ability to burn stored fats.
Pomroy also recommends one day of strength training during this phase, lifting heavy weights for a low number of reps, to help build muscle.
Phase 3 (days 5-7): moderate-carb, moderate-protein, high-fat
In the third phase, the diet claims to “unleash the burn” by reintroducing healthy fats into your diet, while still encouraging moderate consumption of carbs and lean proteins. The idea is that the fats will really kick your metabolism into high gear, says Pomroy.
Pomroy recommends stress-reducing exercise in this phase. She says that yoga and meditation are great options, and that getting a massage also counts.
Can ‘The Fast Metabolism Diet’ help you lose weight?
In the short-term? Probably. Eliminating so many foods means you’ll likely be in a caloric deficit, which is what accounts for the weight loss people see on the diet, says says Abby Langer, R.D., a Toronto-based dietitian.
Still, cycling macronutrients may not be necessary to keep your metabolism humming. There’s no research that shows its beneficial to “surprise the metabolism” and “keep it guessing,” says Langer.
As for those supplements: “You know, most of us don’t need supplements at all,” she says. “Some vitamins, such as B vitamins, are used in energy metabolism, but we get those in so many different foods, deficiencies are rare if not nonexistent in healthy people.”
Another thing to be wary of: The program boasts that some participants lose 20 pounds in 28 days. But, according to the Centers for Disease Control and Prevention, “evidence shows that people who lose weight gradually and steadily (about one to two pounds per week) are more successful at keeping weight off.”
So, the rapid weight loss seen on the program is likely not sustainable—or entirely healthy.
“[This diet is] probably not dangerous physically,” says Langer. Still, the program’s many rules may trigger “disordered eating or unnecessary fear of food,” she says. Langer also calls into questions the diet’s claim that it can help reduce stress, too—something she says a diet isn’t likely to do.
The bottom line: If you’re looking to lose weight or have more energy, you’re better off just eating a balanced diet (with a slight caloric deficit) and exercising regularly.