When analyzing results of the weight-loss trials, researchers found that when dieters increased their protein intake -- even slightly from 18% to 20% of their daily food intake -- while following a calorie-restricted diet, it had a substantial impact on the quality food choices made by the person.
Weight-loss regimens that employ calorie restrictions can often cause dieters to reduce the intake of healthy foods that contain micronutrients such as iron and zinc, noted researchers who found the opposite effect when dieters increased their intake of protein, leading authors of the study to study the link between protein intake and diet quality.
Analysis of food records and diet quality for this study was funded by the Institute for the Advancement of Food and Nutrition Sciences in Washington, D.C.
“The impact of self-selected dietary protein on diet quality has not been examined before, to our knowledge, like this,” said Anna Ogilvie, co-author of the study and a doctoral student in the Department of Nutritional Sciences at Rutgers SEBS.
“Exploring the connection between protein intake and diet quality is important because diet quality is often suboptimal in the U.S., and higher-protein weight loss diets are popular.”
To find a link between protein intake and diet quality, researchers collected data from more than 200 men and women between the ages of 24 and 75 with a body mass index that categorized them as either overweight or obese participating in clinical trials at Rutgers University.
All participants were encouraged to lose weight by following a 500-calorie-deficit diet for six months and allot at least 18% of their caloric intake to lean protein such as poultry, unprocessed meat, fish, legumes, and dairy complemented by fruit, vegetables, and whole grains. Conversely, participants were discouraged from consuming saturated fats, refined grains, sugar, and salt.
Participants kept detailed food records, which researchers analyzed for diet quality, specific categories of foods consumed and ratios and specific sources of protein.
From participants' food records, researchers divided participants into two groups: a lower-protein approach with 18% of overall calories coming from protein (a collective average of 58g/day) or a higher-protein approach with 20% of overall food intake coming from protein (79g/day).
After analyzing all 207 participants' food intake, researchers found that while both low- and high-protein intake groups lost the same amount of weight (about 5% of their body weight over six months), the higher-protein group chose a mix of healthier foods more frequently and consistently.
The higher protein group increased their intake of green vegetables and cut back on sugar and refined grains while being able to retain lean muscle mass over the course of six months.
“It’s somewhat remarkable that a self-selected, slightly higher protein intake during dieting is accompanied by higher intake of green vegetables, and reduced intake of refined grains and added sugar,” commented Sue Shapses, author of the study and a professor of nutritional sciences at the Rutgers School of Environmental and Biological Sciences (SEBS). “But that’s precisely what we found.”
Findings from the study might also assist health professionals when counseling patients on weight management and weight loss strategies, noted researchers.
Researchers added that its analysis and findings led to more questions around protein intake and diet noting, "Although the findings in this pooled analysis indicate that only dietary protein explained the variability in lean body mass changes during calorie restriction, the link to other food choices should be explored as a possibility in future studies.
"Accordingly, it would be interesting to determine whether higher self-selected protein intake that improves diet quality, compared with a protein supplement alone, differentially affects LBM or other health outcomes."
Authors: Anna R. Ogilvie, et al.