Will caffeinated drinks help suppress my appetite?

Thursday, August 02, 2018. Author Dr Haran Sivapalan

Will caffeinated drinks help suppress my appetite?

From nicotine to amphetamines, recreational drugs have often been used for their ‘anorectic' properties; that is, their ability to suppress the appetite. Throughout the 1940s and 50's, someone wishing to lose weight could easily consult a doctor and be prescribed a ‘rainbow diet pill' – a cocktail of amphetamines, thyroid hormones, and diuretics designed to promote weight loss alongside ‘downers' such as benzodiazepines and barbiturates to curb insomnia.

Unsurprisingly, as a result of their addictive and cardiovascular side-effects, rainbow diet pills were banned by the FDA (Food and Drug Administration) in the late 1960s. Today, a much more widely used stimulant drug is often used to suppress appetite; and you can obtain this one without a prescription: caffeine.  

Caffeine and appetite suppression

Caffeine has long been thought to aid weight loss, and several different theories have been proffered to explain this effect. One theory suggests that caffeine enhances fat burning and thermogenesis: the burning of calories to generate heat energy. On this note, one small study found that caffeine can increase total energy expenditure (in kJ) by 5-22% in lean subjects and by 5-10% in overweight and obese subjects.

Another leading theory is that caffeine is, like amphetamine, an appetite suppressant. Far from being a simple function of how much food is in your stomach, your appetite is strongly influenced by a complex interaction of hormonal signals both in the gut and brain. Some of these hormones alert you that you're hungry, while other hormones, called ‘satiety signals', tell you that you're full.  Two such satiety signals are PYY (Peptide YY) and GLP-1 (Glucagon-like peptide 1), and caffeine may transiently increase levels of these hormones, thereby curbing appetite. 

There's also evidence that caffeine speeds up ‘gastric emptying' - the rate at which food is emptied from your stomach into your small intestine, another factor thought to influence how full you feel after eating. A study found that the time taken for half of a meal to pass into the small intestine was 16 minutes quicker after drinking a coffee.

In principle, and from a purely physiological perspective, this all supports the role of caffeinated beverages as potentially useful appetite suppressants. Nevertheless, human appetite is a complicated affair: a meal that fills us up at one time will barely sate our hunger at another time. So, does drinking caffeine cause people to eat less in the long term? 

What does the science say?

A review of the literature found that caffeine may slightly reduce people's food consumption during a single meal. Ingesting caffeine between 0.5 and 4 hours before a meal was shown to reduce energy intake to the tune of around 100 calories (430kJ).  As to why this is the case, the review found no firm evidence that caffeine influences levels of gut hormones, gastric emptying or even perceptions of appetite.

Furthermore, eating less at a single meal doesn't necessarily mean you'll eat less over the course of a day. Indeed, a recent study, published in the Journal of the Academy of Nutrition and Dietetics, followed 50 people over the course of a month and monitored their daily caloric intake. Participants were given a juice drink with either no, 1mg/kg or 3mg/kg caffeine. The lucky subjects were then let loose on a breakfast buffet, instructed to eat as much or little as they wished. 

Compared to the groups drinking no or 3mg/kg caffeine, those ingesting 1mg/kg of caffeine (which is about the amount in a single shot of espresso for a person weighing 65kg) consumed 70 fewer calories at the breakfast buffet.

Later in the day, however, this group overcompensated and ate more, leading to no significant differences in calorie intakes between the different groups.  Moreover, caffeine intake was not associated with subjects' personal reports of changes in their appetite. It appears then, that caffeine isn't an effective appetite suppressant and any effect it does have on food intake are only short-lived. 

Bear in mind, also, that any transient appetite suppression will depend on how fast you metabolize and clear caffeine. Although none of the above studies investigated differences in caffeine metabolism (which is strongly influenced by your CYP1A2 gene), it's plausible that fast metabolizers experience even less of a decrease in appetite, as they clear caffeine from their body more quickly. 

Are there other ways to suppress my appetite?

Yes - increasing your protein intake at breakfast has been shown to boost satiety and keep people feeling fuller for longer throughout the day. Fiber has also been demonstrated to improve satiety, so, if you are looking to avoid that unhealthy mid-morning snack, high-fiber foods such as oatmeal, bran flakes, and fruit are all good breakfast additions.

These nutrition tips may be especially important depending on your genetic make-up. Variants of genes such as the FTO, NMB, and MC4R may predispose you to have a larger appetite, thereby putting you at a higher risk of overeating and weight gain.

I hope you enjoyed this blog.  Please read my other articles and let me know if you have any questions.

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