The report, which dates from last March, adds more weight to the argument that 'bogus' weight loss supplements are damaging the overall industry.
Mintel values the US weight control market - including supplements and foods - at $3.7bn.
However, the market has been in decline since 2002, on the back of a negative consumer perception of diet pills, said the market researcher.
This has resulted from a number of recent issues in the news, such as ingredient bans (ephedra), personal injury lawsuits, Federal Trade Commission (FTC) fines for false advertising, and manufacturer bankruptcies.
The recent petition from drug firm GlaxoSmithKline requesting that weight loss claims be considered disease claims can only exacerbate the situation.
Regardless of whether or not the nation's regulator accepts the petition, the negative media attention gathered is sure to leave its mark on weight loss supplement sales.
Launches this year According to data drawn from Mintel's Global New Products Database (GNPD), there have been 29 new weight loss supplement products launched in the US from January to May 2008.
Last year, GNPD recorded a total of 59 new weight loss supplement launches.
The food category for weight loss recorded 167 new products in 2007 and 94 new products in the 2008 year to date.
Volatile sales According to Mintel, liquid and powder meal replacement drinks have dominated sales in the weight loss category, but this segment has also seen declined sales between 2004 and 2006, "reflecting the market's overall poor performance".
"However, the growing rate of obesity (…) among all gender, age, and ethnic demographics means that weight control products have a wide-ranging market base, if only product claim and ingredient controversies are avoided," wrote Mintel in its Weight Control Products report last March.
According to Mintel, rulings against weight control product marketers are the primary factor impacting sales.
"The FTC has prosecuted over 100 such cases since 1990, and by all indications appears to be tightening its regulatory methods in the near future.
Furthermore, consumer worry about physical side effects and dependency also mitigate sales."
Another factor that helps drive sales includes the high failure rate of dieting.
Women specifically are the most likely to diet and use diet aids, although they are also the most likely to fear dependency and physical side effects, said the report.
Future & opportunities Mintel said that obesity will continue to drive weight loss product sales, although the market is expected to decline one percent at current prices and 12 per cent at constant prices from 2006 to 2011.
By comparison, from 2001 to 2006, total US sales of weight control products decreased by 6 percent at current prices and decreased 18 percent at constant 2006 prices.
However, Mintel also suggested that with the proper messages, there could still be hope for the weight loss category.
"With the rapidly growing number of older adults, the weight control industry should shift a substantial part of its focus away from "rapid weight loss" messages that tend to attract younger adults and towards a message of maintenance and control," it said.