Dear Dr. Blonz: Two weight-loss “miracles” are featured in a constant stream of emails I now receive. (I take responsibility for this mess, having clicked on an ad a few weeks ago.) One of the ingredients is hoodia, and the other is Caralluma fimbriata. The ads discuss how they have been used for centuries in India to suppress appetite. There is also mention of research studies providing evidence that they work to cause weight loss. Are these something you are familiar with? — M.Q., Lafayette, California

Dear M.Q.: Hoodia gordonii is a succulent plant found in Africa. There is no reliable scientific evidence to affirm the weight-loss efficacy of hoodia. The Federal Trade Commission has taken action against a company for making false weight-loss claims about hoodia.

Caralluma fimbriata is the name of a succulent plant that does, indeed, grow in India. It can be eaten raw or cooked with spices, but it’s also used in pickles and chutneys. Stories in folklore tell of chewing chunks of this plant to suppress hunger while on days-long hunts.

There is a published, peer-reviewed study for Caralluma fimbriata. The details of this study can illustrate how folkloric stories, coupled with aggressive marketing, will not guarantee that a product works.

The research was published in the May 2007 issue of the journal Appetite, and it involves a 60-day study using 50 overweight male and female volunteers. Half the subjects received an extract of Caralluma fimbriata, and the other half received a placebo. Measurements were taken before, midway and at the end of the study, including weight and BMI (body mass index) and body fat, along with appetite variables such as food intake, measures of hunger, thoughts of food and feelings of fullness.

At the end of the study, the group taking Caralluma fimbriata had lost weight, and their BMIs (and a number of other measurements) were lower. I have seen this mentioned in advertisements. But — and this is key — what the ads leave out is the fact that similar results were found in the placebo group.

This reinforces why it is absolutely essential to have a placebo group when studying the possible efficacy of substances. Comparing both groups, there was no significant difference in body weight, BMI, body fat or hip circumference. The only difference between the groups was in the measure of waist circumference — but, given the lack of difference in all other metrics, this is of dubious import.

The Appetite study reported no differences in thoughts of food, feelings of fullness, urges to eat or in the amounts of energy (calories), fat, carbohydrate and protein consumed. The only difference between the groups was in reports of hunger. Even so, when compared to the placebo, the treatment did not have a significant effect on how much the subjects actually ate.

Our bottom line is that there is nothing “miraculous” to report about Hoodia gordonii or Caralluma fimbriata as weight-loss products. A second important takeaway is that we always need to view these types of claims with a critical eye.

Ed Blonz, Ph.D., is a nutrition scientist and an assistant clinical professor at the University of California, San Francisco. He is the author of the digital book “The Wellness Supermarket Buying Guide” (2012), which is also available as a free digital resource at blonz.com/guide.

Send questions to: “On Nutrition,” Ed Blonz, c/o Andrews McMeel Syndication, 1130 Walnut St., Kansas City, MO, 64106. Send email inquiries to questions@blonz.com. Due to the volume of mail, personal replies cannot be provided.