When weighing the benefits of one weight-loss plan over another, dieters may want to consider what else might be cut with the calories and carbs, suggests a new study.

More than $30 billion a year is spent on weight loss products in the U.S., with one in three adults reportedly trying to trim pounds.

The focus of these popular diets typically rests on both the overall amount of food consumed and the relative quantities of proteins, fats and carbohydrates. Vitamins and minerals tend to be overlooked.

In a comparison of four weight-loss plans, researchers from Stanford University in California found significant differences in the consumption of these nutrients.

“Shifting around the food sources that are good sources of fats versus carbohydrates means more than just changing fat and carbohydrate levels,” lead researcher Christopher Gardner told Reuters Health in an email.

Varying amounts of vitamins and minerals tag along, he said. And, as a result, deficiencies can arise that increase the risk of serious health problems, including low blood count, the bone-thinning disease osteoporosis and neurological damage.

In the study, Gardner and his colleagues looked at data from 300 overweight or obese women who were randomly assigned to follow one of four weight-loss diets: Atkins, Zone, LEARN (Lifestyle, Exercise, Attitudes, Relationships, Nutrition) or Ornish.

The women each received three unannounced phone calls around the start of the study and again after 2 months, asking them to recall what they had eaten over the previous 24 hours. These responses were then averaged to get a precise picture of the woman’s diet, report the researchers in The American Journal of Clinical Nutrition.

At 2 months, participants across all diets had similarly reduced their daily intake to 1500 calories from an average of 2000 at the start of the study. (Each pound of weight loss requires eating 3,500 fewer calories.)

As expected, the team found differences in what dieters ate consistent with each diet’s design. Atkins dieters, for example, reported eating the lowest proportion of carbohydrates (17 percent of their daily calories) and the most fat and protein (28 percent).

Differences were also seen in how much of 12 of the 17 vitamins and minerals measured the dieters were eating, leaving some women at risk of inadequate levels based on national recommendations. Vitamin E posed the biggest problem across all groups: more than 65 percent of women weren’t getting enough.

With people eating less, it may come as no surprise that they were also missing out on vitamins and minerals. But for women on the Zone diet, the opposite was true. Risks of inadequacies significantly decreased for vitamins A, E, K and C, while no increased risks were seen for any other vitamins.

The researchers suggest this points to the potential benefits of a diet that encourages moderate but not extreme carbohydrate reductions: down to 40 percent of total calories from traditional recommendations of 45 to 65 percent.

“It isn’t just total carbohydrates that Zone recommends be cut back. It is more specifically the added sugars and refined grains,” said Gardner. “Keep the greens and beans and veggies. Lose the soda, sweets, and the packaged processed foods.”

One potential way to fill in the holes of any diet is through vitamin and mineral supplements, he added. But the researchers found that, of the four diets, only Atkins made this recommendation. And only 3 women in this group took the advice.

“Our bodies work best when vitamin and mineral deficiencies are absent, and healthy food is the best way to get enough of these important nutrients,” Dr. Michael Dansinger of Tufts University School of Medicine in Boston, and advisor for the television series “The Biggest Loser,” told Reuters Health by email.

“I believe all the eating strategies in the Stanford study are healthy because they improve obesity, diabetes and heart disease risk factors, which are the leading killers in our society,” Dansinger said. “However, the Zone diet, and others like it, may have an advantage where vitamins and minerals are concerned.”

SOURCE: The American Journal of Clinical Nutrition, online June 23, 2010.