While patients who are dieting to reduce body weight might try to maintain protein intake, protein levels often fall below what is recommended.

Although previous studies have reported on the effects of higher protein intake on health outcomes during weight loss, little is known about how diet quality changes due to different levels of protein intake when dieting for weight loss.

“When people are dieting to reduce body weight, they may cut all components of the diet, including protein,” explains Sue Shapses, PhD, RD. “While patients might try to maintain protein intake, protein levels often fall below what is recommended,” she says. “This is a problem because patients may be compromising on other healthy food options in their diet compared to those who have a higher protein intake.”

Known Health Benefits Linked With Higher Protein Intake

Understanding the link between diet quality and protein intake during weight loss is important because there are known health benefits associated with higher protein intake, says Dr. Shapses. “We know that adequate or moderately higher protein intake is important,” she says. “However, clinicians might not always think about how other foods in the diet—specifically, low- or zero-protein foods—are simultaneously changed. And these low- or zero-protein food changes may happen to have benefits, such as greater intake of green vegetables and lower intake of refined grains and sugars. “

For a study published in Obesity, Dr. Shapses and colleagues examined how changes in self-selected protein intake during caloric restriction (CR) altered diet quality and lean body mass (LBM). They performed a pooled analysis of completed trials in which 207 overweight or obese participants underwent similar protocols for moderate weight loss. Lifestyle modification counseling was delivered in 16 group sessions over 6 months, and patients were examined before and during 6 months of CR. Diet quality was assessed using the Healthy Eating Index in patients with lower or higher protein intake.

Increasing Protein Intake Yields Important Benefits

On average, study participants lost 5% of their baseline body weight. During CR, the lower protein group in the study consumed an average of 58 g/d, compared with an average of 79 g/d for the higher protein group. Those with higher protein intake during CR had a greater improvement in diet quality when compared to those in the lower protein intake group. Both groups lost a similar amount of weight and fat mass during CR, but there was a greater decrease in LBM in the lower protein group than in the higher protein group (Figure).

These findings suggest that a moderately higher protein intake during CR improves diet quality and diminishes loss of LBM. “Increasing the level of protein intake from the recommended 0.8 g/kg/d—or 18% of calories—to a moderately higher intake of 1.0 g/kg/d—or 20% of calories—has significant effects on the quality of the diet, as measured by the Healthy Eating Index,” Dr. Shapses says. “It also altered the composition of weight loss to attenuate LBM.” Overall, weight loss in people who consumed higher protein levels mitigated loss of LBM, but also altered low- or zero-protein foods, which improved diet quality.

Remind Patients About Protein Goals While Dieting

According to Dr. Shapses, protein intake is often lower among middle-aged and older adults, especially in women, who are dieting. “It’s important to remind patients that their protein goal should be about 20% of the calories from protein to attenuate loss of LBM while dieting,” she says. “Of note, all subjects in our study were encouraged to stay physically active on their own. Higher protein intake is unlikely to attenuate loss of LBM if it is not accompanied by exercise. Another reason it’s important to reach this protein goal is that it could potentially benefit bone, too.”

Understanding how to preserve LBM during CR continues to be an area of active research. “Since a higher protein intake in our study was largely from low-fat animal sources, it would be interesting to see if results are similar if the primary source of protein was from plants, such as soy or other legumes,” says Dr. Shapses. “Furthermore, studies are needed to determine if responses to dietary shifts are similar in people who consume different ethnic foods and in vulnerable populations, such as children and the elderly.”

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