“At a daily energy intake of 2000 kcal, the three diets did not provide recommended intakes [or less than 90% of Dietary Reference Intake (DRI)] of at least two micronutrients (vitamin D + calcium or B12),” the researchers wrote in their report, published in the journal Nutrients.
Additionally, across all the analyzed plans, vitamin D was less than 30% of the Dietary Reference Intake of 600 IU/day.
The researchers specifically looked at diets that were received top reviews on Amazon and were marketed for long-term lifestyle changes as opposed to rapid weight loss within a short period of time.
Most weight-loss diets restrict intakes of energy and macronutrients, but overlook micronutrient profiles. Hence, the researchers sought to evaluate micronutrient sufficiency in three popular diet plans.
“Diet books are used largely unsupervised by a health professional,” Dr. Tom Brenna, co-author of the study and a professor of human nutrition and pediatrics at the University of Texas at Austin, told NutraIngredients-USA. “They should clearly indicate that micronutrient deficiencies are possible if the diets are faithfully over a many month period.”
In addition to Dr. Brenna, the co-authors one researcher, Matthew G. Engel, of Cornell University, and two employees of supplement manufacturer The Nature’s Bounty Co., which partly funded the study. Dr. Brenna is a member of the company’s Scientific Advisory Council.
Study Design: Looking at weight loss and weight maintenance diets
The researchers browsed through the top-reviewed diet books on Amazon.com on December 18, 2016.
The selected plans included “Eat to Live-Vegan, Aggressive Weight Loss,” and “Fast Metabolism Diet” to represent two genres of commercial weight-loss diets, hypocaloric vegan and high-animal-protein low-carbohydrate diets.
A third diet plan, “Eat, Drink and Be Healthy,” was included in the diet analysis to be representative of weight maintenance diets.
Then, the researchers looked at seven single-day menus of each diet to represent one week of menus on each diet regimen. Sample menus were manually entered into the online nutrient tracker Cron-O-Meter, a web-based nutrition and biometric tracking application which features data on over 60 nutrients and contains more than 7,500 foods in its databases.
Results: “Diets designed for specific groups and purposes can benefit from some level of dietary supplementation”
The nutrition profiles of the sample menus were compared to micronutrient sufficiency based on US Dietary Reference intakes for male US adults.
Without adjusting for energy intake, the “Eat to Live-Vegan, Aggressive Weight Loss” plan failed to provide 90% of recommended amounts for vitamins B12, B3, D, E, calcium, selenium, and zinc. The “Fast Metabolism Diet” was low in vitamins B1, D, E, calcium, magnesium, and potassium, while the “Eat, Drink and Be Healthy,” met DRIs for all but vitamin D, calcium, and potassium.
Several limitations included assumptions made for serving size when such information was missing or unspecified, as well as estimating how long dieters will adhere to a program.
“Most evidence over the years has shown that people have difficulty adhering to diets permanently. That is, most people stop diets and gain the weight back,” Dr. Brenna said.
“As to whether nutrient deficiencies may be an issue, we should consider that the intention of commercial diets is to limit caloric intake over an extended period. Insofar as adopters adhere to the diet, they may be vulnerable.”
Communicating the message to dieters
“As this study shows, even diets designed for specific groups and purposes, such as weight loss, can benefit from some level of dietary supplementation in order to fill nutrient gaps and help prevent important micronutrient deficiencies,” said Mark Gelbert, Chief Scientific Officer at The Nature’s Bounty Co.
“It is our commitment to wellness to provide consumers with objective, fact-based resources that help them make informed decisions regarding nutrition.”
Dr. Brenna added: “Even low weight maintenance diets that are of generally low risk of deficiency should indicate that foods should be carefully chosen so as to provide a balanced nutrient profile. Responsible diet books do in fact mention this.”
Published online, doi:10.3390/nu10010108
“Micronutrient Gaps in Three Commercial Weight-Loss Diet Plans”
Authors: Matthew G. Engel, Hua J. Kern, J. Thomas Brenna, and Susan H. Mitmesser