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Bitter-tasting plants have a long history as traditional health-giving foods and medicines, with recent interest in their application as appetite suppressants. To examine this potential effect, Edward Walker, PhD, of the New Zealand Institute for Plant and Food Research in Auckland, and colleagues conducted a small randomized, double-blind, cross-over treatment study.

As the researchers described in the study in , the participants, 30 healthy lean adult women, mean age about 21, were required to fast for 24 hours from 6 pm to 6 pm on three occasions and given an ad libitum meal to break each fast.

Treatments of either a placebo or one of two doses (high dose of 250 mg or low dose of 125 mg) of the bitter hops–based appetite suppressant Calocurb (main ingredient Amarasate) were given twice a day at 16 and 20 hours into the fast.

This bioactive extract has exhibited appetite-suppressing effects by increasing blood concentrations of anorexigenic gut chemicals, the researchers explained.

The intervention groups had a significant (P<0.05) reduction in appetite and cravings for food compared with the controls. Relative to placebo, energy intake at the post-fast ad libitum meal was 14.3% lower with the high-dose treatment and 8.1% lower with the low-dose treatment.

That finding suggests that appetite suppressant co-therapy may reduce hunger in fasting women, and that gastrointestinal delivery of bitter compounds may be an effective method of cutting food cravings, the investigators said.

Walker elaborated on the findings in the following interview.

What did your group hope this study would reveal about the use of this extract in women?

Walker: We really wanted to measure the effectiveness of this hop extract on appetite in females and provide evidence to support its use in dietary interventions.

Women are often excluded from these kinds of acute studies examining appetite and food cravings because you must schedule each study day on the same day of their menstrual cycle -- that is, you can only do one study day per month, depending on menstrual cycle length. This means that studies in females take longer, are more difficult, and cost more money. This often leads to studies being conducted only in males, which is alarming when you consider how different both appetite and craving profiles are between males and females.

There is also evidence suggesting that this extract may be more effective in women -- for example, because they have increased sensitivity to bitterness and are more sensitive to the appetite-suppressing mechanisms we are targeting.

What is the mechanism of action?

Walker: In a previous clinical trial, we showed that bitter hop extract works by stimulating the release of several appetite-suppressing hormones from the gut. These hormones include three major appetite suppressants such as glucagon-like peptide-1, cholecystokinin, and peptide YY, all of which act together to reduce hunger and delay gastric emptying and also have roles in glucose control and regulation of gut motility.

Were the effects in this cohort of women more pronounced than in men who have been studied?

Walker: Yes, when you compare the results with those of the previous study done in males, there was a noticeably greater effect in females. We report an approximately 50% greater effect on hunger in females and see greater decreases in cravings for food and post-fast cravings for sugary foods. The extract is very effective in the female cohort.

How did you measure cravings/appetite levels?

Walker: We used visual analogue scales, the gold standard for assessing changes in subjective measures of appetite. Essentially, you ask a question -- for example, "How hungry are you feeling?" -- and get the participants to make their response on a 100-mm line anchored with "Not at all" on one end and "As hungry as I have ever been" on the other.

Are these extracts readily available to consumers or are they experimental?

Walker: Calocurb, the extract used in this study, is available as a commercial product. It has been through a safety review and has GRAS [generally regarded as safe] status for up to 500 mg per day -- the same amount as the high-dose treatment in this study.

The study women were fasting, but could this extract likely work well in non-fasting persons on a reduced-calorie regimen?

Walker: Absolutely. This study was designed as a challenging test to see if the extract would work when hunger and cravings were extreme. It is highly likely that similar reductions in appetite and cravings would be observed in the context of a more conventional reduced-calorie intervention.

How is the extract taken and are there any contraindications?

Walker: This oral treatment is gut-targeted and needs to be taken on a relatively empty stomach at least an hour before the next meal so it reaches the correct part of the gut before the capsule opens. Because it is gut-targeted, the suggested contraindications are major gut diseases such as inflammatory bowel disease. Conditions like irritable bowel syndrome [IBS]-diarrhea may need to be managed, since the most frequent side effect of the supplement is loose stools and treatment may acutely worsen existing IBS symptoms.

Is there any danger to taking this extract for weight control over the longer term?

Walker: There are no indications that long-term safety would be an issue. This extract has been available in certain markets for 6 years and has been used consistently since then by many people. There are some mild gastrointestinal side effects such as heartburn that may present when people are first taking it, although these typically resolve after a few days of use.

What other research is underway?

Walker: We currently have a weight-loss trial underway, and in the future we will be doing more research focused specifically towards "in need" populations such as postmenopausal women.

Additionally, we'll be exploring the extract's role in glucose control. Some medical practitioners are conducting smaller in-clinic studies evaluating this extract as a pre GLP-1 receptor agonist option, as a co-therapy to allow for lower GLP-1 receptor agonist dosages to be used, and also as a post-treatment agent to prevent rebound weight regain.

Is there a hopeful message in the findings for persons with obesity?

Walker: Yes, there is a clinically validated nutraceutical that may be useful in managing appetite and cravings during dietary change. This product may be a useful tool to improve the overall success of GLP-1 receptor agonist–based treatment protocols, particularly when patients are coming off the injections.

Read the study here and expert commentary about it here.

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