While many Americans restrict or alter their diets to improve their overall health, research suggests that dietary restriction does not always lead to a high-quality diet, according to a study published in Current Developments in Nutrition.

Study details and key findings

For the study, researchers analyzed dietary data from 34,411 individuals 20 and older who participated in the National Health and Nutrition Examination Survey between 2005 and 2018.

To evaluate participants' dietary intake, researchers used the National Cancer Institute's intake methodology. Notably, they did not ask participants' to report a specific diet they were following. According to previous research, most people do not accurately categorize their diet. To accurately assess participants dietary patterns, the researchers tracked the food and nutrients participants were consuming.

They then compared participants' eating habits to NIH's recommendations and created seven diet categories, which included restricted carbohydrate, low-grain, high-protein, vegetarian, pescatarian, and time-restricted. They also created a general population diet, which did not fall within the parameters of the other diet categories.

To assess diet quality, they used the 2015 Healthy Eating Index, which measures diets on a scale of zero to 100.

While most of the diet patterns received a failing grade, the diets ranked by quality included pescatarian (65.2 out of 100), vegetarian (63 out of 100), low-grain (62 out of 100), general population (57.1 out of 100), restricted-carbohydrate (56.9 out of 100), time-restricted (55.2 out of 100), and high-protein (51.8 out of 100).

The researchers also modeled each diet pattern to measure the impact of replacing one serving of food high in sugar, sodium, saturated fat, and refined grains with alternative foods.

After substituting foods high in fat, sugar, salt and refined grains with alternatives, the researchers found that the highest increase in diet quality occurred with the high-protein diet, which saw a 9.8 increase. However, other diet patterns saw a smaller impact, with 3.9 points for the vegetarian diet, 3.1 for time-restricted, 3 points for pescatarian, 2.4 points for restricted-carbohydrate, and 2 points for low-grain diet patterns.

Commentary

Ultimately, the study's findings suggest that restricting or replacing one food group with another does not necessarily lead to a high-quality diet. The researchers found that quality scores did not increase significantly when certain foods were replaced with alternatives.

"What occurred to us is that most people are consuming their foods as mixed dishes that contain multiple ingredients," said lead study author Zach Conrad, a nutritional epidemiologist and assistant professor at William & Mary College. "Some of these ingredients are healthy and others are not, so swapping these mixed dishes led to an increase in both healthy and unhealthy ingredients. The overall effect was still positive, but a lot of it washed out."

"For example, take pizza. It's a good source of dairy and provides some vegetable toppings, but it's also rich in saturated fat, sodium and refined grains," Conrad said. " Replacing refined grain pizza with whole-grain pizza will make it healthier, but you're still left with the saturated fat and sodium. It's all about trade-offs."

"There is more than one way to eat an unhealthy diet," he added.

Still, Conrad noted that even small, sustainable changes can have a positive impact on a person's long-term health—even if results are not immediate. (Gans, U.S. News & World Report, 11/7; Conrad et al., Current Developments in Nutrition, 9/12)