Chilli peppers 'help to burn fat'

“A sprinkling of red chilli peppers on your dinner keeps hunger pangs at bay,” reports the Daily Mail. It said that spicing up a daily diet with chopped chilli peppers could help curb your appetite.

The effects of capsaicin, the chemical that makes peppers and chillies hot, have been studied again in a small trial investigating what effects hot red (cayenne) pepper has on energy expenditure, body temperature and appetite. It used doses that people would normally eat and found that 1g of pepper reduced cravings for salty, sweet and fatty foods and increased energy expenditure. It noted that this effect was greater among the 12 trial participants who did not normally eat spicy peppers compared with the 13 who reported being regular users.

The study was reliably carried out but is very small, with only 25 participants. In particular, the differences between regular and non-users need confirmation in larger studies. Although the news has related this to possible dietary benefits in people trying to lose weight, the participants were all healthy young people of normal weight. This is early preliminary research and further study is needed.

Where did the story come from?

The study was carried out by researchers from Purdue University, in the US. Funding was provided by the National Institutes of Health through a National Research Service Award, and the McCormick Science Institute. The study was published in the peer-reviewed medical journal Physiology and Behavior .

In general, the press accurately represent the reporting of this study. However, as the study was conducted in people of normal healthy weight, the suggestion that chillies may be of benefit to people trying to lose weight is an assumption that should not be made on the basis of the current study alone.

What kind of research was this?

This was a small, randomised crossover trial, in which the researchers investigated the effect of cayenne red pepper consumption during a meal on skin and body temperature, energy expenditure and appetite levels after the meal. Previous studies have suggested that red peppers (and in particular capsaicin, the chemical that makes peppers and chillies hot) suppress hunger and make the body generate heat. However, these studies have often used more hot pepper or chilli than the average person would choose to eat (for example, 10g/meal, when a person would normally choose to consume about only 1g/meal). This study aimed to test more acceptable cayenne pepper doses consumed during a single meal. In the crossover design, the recruited participants tried, in a random order, three amounts of pepper with their meal: a standard quantity, their chosen quantity or none.

What did the research involve?

The researchers recruited 35 participants through public advertisements, who were all young (with an average age of 23 years) and had a healthy body weight (BMI 22.6). To be eligible, participants had to be in good health, non-smokers, have a stable weight and have steady dietary and activity habits. Of these 35, the researchers report results for only 25, as three dropped out before the study began, and seven dropped out for various reasons (for example, intolerance to chilli or unwillingness to abstain from caffeine) during the study. The 25 included 13 who reported regularly eating spicy food and 12 who did not.

Participants attended the study centre for six meal visits, one week apart. For three days before each visit the participants were advised to eat either a high-fat diet (before two visits), a high-carbohydrate diet (before two visits) or their normal diet (before two visits). They also had to avoid alcohol, caffeine or strenuous physical activity on these days. On each test day, the participants were asked to arrive an hour before lunchtime, having fasted for 12 hours beforehand. Physiological tests of their resting energy expenditure, body and skin temperature, and appetite were then taken.

The participants’ chosen quantity of cayenne pepper was added to the meal after the two three-day periods in which they had eaten their normal diet (on average 1.8g/meal was chosen by regular spicy food users and 0.3g for non-users). After the two three-day periods in which they had been eating a high-fat diet, and the two in which they were eating a high-carbohydrate diet, they were randomly assigned to receive either a standard amount of cayenne pepper (1g per meal) or no cayenne pepper.

The study reports that the doses of pepper were given in either capsule form or “orally” (presumably meaning it was added to the meal in some way). Though it is not clear how the decision to give orally or by capsule was made (for example, whether it was made randomly on each of the six attendance days or whether participants were assigned to receive the pepper orally on set days and by capsule on others). On the days when no pepper was given, the researchers say that this was by the use of a plain dummy capsule.

The participants ate all meals until comfortably full. During a four-and-a-half-hour period after the meals, their energy expenditure, body and skin temperature, and appetite were again assessed at intervals. Appetite had been assessed at 30-minute intervals using a validated appetite questionnaire with responses such as hunger, fullness or desire to eat rated on a visual analogue scale.

What were the basic results?

Compared with eating no pepper, the standard 1g dose of cayenne pepper significantly increased body temperature by an average of 0.02°C (regardless of the preceding three-day diet). Skin temperature decreased by an average of 0.11°C after the high-fat diet and by 0.23°C after the high-carbohydrate diet. Skin temperature was also lower when the pepper was consumed in capsule rather than oral form, but this had no effect on body temperature. The effects on body temperature did not differ between regular and non-users of spicy food.

Pepper had a greater effect on the appetite in those who didn’t usually eat spicy food compared with people who regularly ate spicy food. Generally, non-users had less desire to eat salty, fatty or sweet foods after eating 1g pepper than those who ate spicy food regularly. There was no difference in effect on appetite when the dose was delivered orally or via a capsule.

There was an increase in energy expenditure (of about 10kcal) following ingestion of 1g of pepper compared with no pepper. While there was no significant difference in energy expenditure between regular and non-users, (i.e. both user groups increased energy expenditure after eating the pepper), the researchers noted that the greatest effect on energy expenditure occurred when non-users took the pepper in oral form (rather than by capsule), and the lowest effect occurred when regular users consumed it in either capsule or oral forms.

How did the researchers interpret the results?

The authors conclude that red pepper has weight management potential. However, they also say that individuals who regularly consume hot red peppers may become desensitised to the effects of red pepper on appetite and energy expenditure.

Conclusion

This study tested the effects of eating hot red pepper at mealtimes on post-meal energy expenditure, body temperature and appetite. It found that, compared with eating no cayenne pepper with the meal, 1g of pepper reduced salty, sweet and fatty food cravings and also increased energy expenditure. The effect was greater in people who did not normally eat spicy peppers compared with those who reported being regular users.

The study is valuable in that it evaluated amounts of hot pepper that are likely to be consumed as part of a normal diet, whereas previous studies have evaluated unusually high amounts of hot pepper. It also investigated the effects of consumption in different subgroups, namely those who were regular and non-users, different pepper doses, people consuming different pre-test diets (high fat, high carbohydrate or normal), and consumption in capsule or oral form. This multiple subgroup testing can be a statistical weakness, as the more comparisons you carry out the more likely you are to find significant differences by chance, but the researchers have made adjustments for this.

In spite of some strengths, this is a small study and can only really be considered to be preliminary research. Only 35 people were enrolled into the trial and of these only 25 completed it.

The main results pertain to the differences between regular non-users and users of spicy foods, but there were only 12 and 13 of these, respectively. Therefore, observed differences between these small groups of people need confirmation in much larger studies to see whether a true difference exists.

In addition, the participants were healthy young people, with a normal BMI. Although the news has said these findings may lead to possible dietary benefits in people trying to lose weight, this has not been tested in this study.

Further randomised trials investigating the effects of supplementary dietary pepper or chilli in people trying to lose weight could be conducted.