Growing research suggests high protein diets help people feel fuller, use more energy, and increase fat loss. Accordingly, high protein total diet replacement products — nutritionally complete foods or drinks designed to replace someone's complete diet for a certain period of time — have recently skyrocketed in popularity.

That's because they're marketed as an intensive method capable of adding extra protein and helping people lose weight fast. If proven effective, these products could be game-changing for people dealing with obesity and its related health effects. But there's a catch: They haven't yet been rigorously studied for efficacy, so scientists can't say for sure they work.

But in a new study, which put high protein total diet replacement head to head against a typical North American diet, researchers grew closer to understanding the power of protein.

Their findings were published in The American Journal of Clinical Nutrition.

In the experiment, healthy people who ate high protein total diet replacement products burned more calories and fat over 32 hours, compared to people on a North American diet — a mix of various carbs, proteins, and fats. The protein group also ended the experiment burning more fat than they consumed, likely implying future weight loss over time.

In the experiment, healthy people who ate high protein total diet replacement products burned more calories and fat over 32 hours, compared to people on a North American diet — a mix of various carbs, proteins, and fats. The protein group also ended the experiment burning more fat than they consumed, likely implying future weight loss over time.

The experiment also offers direct evidence that all calories aren't created equal. "Our study proved that the same number of calories but from different diets can elicit different responses in energy metabolism," study co-authors Carla Prado and Camila Pinto told Inverse in a joint statement. Prado and Pinto are researchers at the University of Alberta.

While the study is limited to healthy people with a normal weight, scientists hope the findings will eventually lead to new interventions for people trying to manage a healthy weight — a step toward a longer life, free of disease.

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HOW THIS AFFECTS LONGEVITY — The team recruited a group of healthy, normal-weight adults between the ages of 18 and 35. Normal weight is defined as having a Body Mass Index between 18.5 and 24.9 kg/m.

Participants were then randomly split into one of two groups: one group was fed the high-protein total diet replacement, which consisted of 35 percent carbohydrate, 40 percent protein, and 25 percent fat. The product is a commercially available supplement comprised of soy protein, yogurt, and honey.

The second group, or control group, was fed a diet with the same number of calories, but consisting of 55 percent carbohydrate, 15 percent protein, and 30 percent fat — what's considered a typical North American diet. Both groups received the prescribed diets for a 32-hour period while inside a metabolic chamber.

Before changing up their diets, the researchers tested participants' body composition, energy expenditures, and metabolism.

On average, the high-protein total diet replacement, when compared to the North American diet, resulted in:

Higher energy expenditure
Increased fat oxidation
Negative fat balance, which implies body fat loss

"These results suggest that normal-weight individuals can have some metabolic advantages when consuming this type of nutritional product," the researchers explain.

It also suggests a higher proportion of protein might be beneficial compared to a diet consisting of the same number of calories, but with a lower proportion of protein.

However, due to the limitations of the study, it's impossible to link the outcomes to protein alone or determine whether there's something unique about the total diet replacement products versus simple proteins like chicken or tofu.

SCIENCE IN ACTION — It's too early to draw practical insight from these findings for daily life just yet. More research is needed — and larger, more diverse groups of people need to be studied — to pinpoint how protein or total diet replacement products impact health or weight loss. But they do shine a light on a path forward.

"Although these results are restricted to a short term and a specific population group, it can help nutrition scientists and health practitioners better understand the real physiological effects of a high-protein total diet replacement in humans," Prado and Pinto say.

Next, the team is also interested in how men and women respond to these dietary changes, as their metabolic regulation "differs considerably," they say.

Ultimately, while protein may not necessarily be an ironclad shortcut to lose weight, it is an essential nutrient for life. And based on the data, eating protein can help people feel satisfied with their meals, increase their energy expenditure, and support muscle mass.

It's not a bad idea to make sure you're getting enough. To determine your daily protein intake, you can multiply your weight in pounds by 0.36, or use this online nutrient calculator.

Some healthy sources of protein are lean meats like fish, nuts, and leafy greens.

Abstract:

Background: High-protein diets and total diet replacements are becoming increasingly popular for weight loss; however, further research is needed to elucidate their impact on the mechanisms involved in weight regulation.