Here are some of the downsides to consider before you try the Ideal Protein diet.

A Long Period of Dieting Usually Isn’t Sustainable

Strict diets can help with weight loss, but the results may not last. “In terms of low-carb diets for weight loss, studies reveal that it produces short-term weight loss; more long-term studies are needed to account for its effectiveness,” says Anderson-Haynes. For example, one review, published in the Medical Clinics of North America in January 2018, noted that while a person can lose weight through a number of methods, keeping the weight off is the real challenge, and that a typical cycle is weight loss, weight plateau, and weight regain.

People May Unnecessarily Restrict Healthy Foods

Certain foods contain important nutrients (hello, produce!), but may be too high in carbohydrates for a low-carb diet. “A low-carb diet requires restriction of fruits, whole grains like rice and pasta, and starchy vegetables like sweet potatoes and corn, all of which are packed with important nutrients like antioxidants, fiber, and micronutrients like magnesium,” says Anderson-Haynes.

And although protein is encouraged on Ideal Protein, many plant-based proteins are discouraged. Take plant sources like legumes, for example, which are associated with a healthy metabolism, past research notes. Those nutrient-packed foods are on the do-not-eat list for Ideal Protein.

You Need to Buy Their Packaged Products

An integral part of the Ideal Protein plan is the company’s packaged foods. For people who may be trying to limit their packaged and processed food consumption, this can be a real problem. Also, packaged food purchases will spike your grocery bill (more on that later).

Ultraprocessed Foods May Be Unhealthy in the Long Run

Indeed, many health professionals encourage a shift away from highly processed packaged foods, which are a key part of the Ideal Protein diet.

review published in the January 2020 Nutrition noted that if you’re trying to lose weight for better health, good, high-quality foods such as whole fruits and vegetables are key. Another study, in the May 2019 BMJ, found that a diet high in ultraprocessed foods, which are involved in the Ideal Protein diet, was associated with an increased risk of cardiovascular disease. A study in the February 2018 BMJ linked these processed foods to an increased breast cancer risk.

Supplements Are Required on the Diet

Another component of the Ideal Protein diet is their branded supplements. They include a multivitamin, a calcium-magnesium supplement, an omega-3 supplement, and a potassium supplement, according to an Ideal Protein affiliate. The U.S. Food and Drug Administration (FDA) does not regulate supplements the same way they regulate conventional medication, and manufacturers can produce and market a supplement without notifying the FDA.

The National Institutes of Health recommends a cautious view of supplements. An editorial published in June 2022 in JAMA Internal Medicine stated that there is little evidence that vitamin and mineral supplements do anything to prevent cancer, cardiovascular disease, or premature death. The author concluded, “In the face of such underwhelming benefits, what explains the number of people who regularly consume these unnecessary supplements?”

Too Much Protein May Not Be Healthy for Some People

“Excess protein carries risk, especially for those with liver and kidney conditions,” says Anderson-Haynes. A review in the August 2020 Journal of the American Society of Nephrology found that high-protein diets affected how the kidneys function in people with or without any preexisting kidney issues.

Protein type matters, too. On the Ideal Protein diet, protein sources include their packaged items like Chicken Chowder, Thai Pork Soup, and Peanut Butter Bar, as well as approved proteins like flank steak, skinless breast, and salmon. “Protein can also affect how the body uses insulin — a study in the American Diabetes Association’s journal Diabetes Care reported that diets high in animal protein can increase diabetes risk,” says Anderson-Haynes.

Veganism Isn’t Possible on the Diet

As the company states on their website, Ideal Protein doesn’t allow for veganism (though vegetarianism is allowed). “This is a major limitation, given the environmental climate, rising cost of food — specifically, animal protein foods — and evidence in research pointing to a plant-forward eating style to improve health and longevity,” says Anderson-Haynes.

Veganism specifically may be helpful for weight. A review published in the September 2022 Obesity Reviews found that a vegan diet may lower body weight, and reduce a person’s A1C, which is a marker for diabetes, and LDL “bad” cholesterol. The review didn’t find a connection between going vegan and lowering blood pressure or raising “good” HDL cholesterol, though.

There’s Not Enough Research on Ideal Protein

There are no studies showing that this specific plan can help people lose weight and keep it off to improve their health. The company claims that weight loss is healthcare, but whether weight loss through Ideal Protein directly helps people become healthier is unproven. Beyond that, the Cleveland Clinic notes there isn’t enough evidence to show the ketogenic diet more broadly is safe over a period of 20 to 30 years.