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Too Good to be True? The Story of Leptin and Ghrelin

Chocolate shot to success in sixteenth and seventeenth century Europe thanks to being both “delicious” and “nutritious and filling” (and if you want to hear more about how smart marketing by the Jesuits and Papacy made drinking chocolate take off around Europe, please come to a virtual tasting).

Fast forward to today, and more and more nutritional wonders are being claimed for chocolate. Many of these studies are based on the discovery of hormones that sound a little like characters from The Hobbit, ‘ghrelin’ and ‘leptin’. Leptin was isolated by Douglas Coleman and Jeffery Friedman in 1994 and helps explain why we feel satiated and full (and then stop eating). Ghrelin was isolated a few years later in 1999 by Masayasu Kojima and Kenji Kangawa and is critical in determining how, and when, we feel hungry (and start eating). And there’s also glucagon-like peptide 1 (GLP1), peptide YY, oxyntomodulin (OXM), orexin, glucagon and a bunch of others (hat tip to Professor Peter Goodfellow for extending this list).

Researchers have performed all sorts of further studies based off these discoveries; measuring for example how just sniffing foods like chocolate impacts leptin and ghrelin levels. See below for a few examples that sound “too good to be true”, and why some scepticism may be called for (hint: check the sample size).  

Plus we’ve details on ZOE, the company running the world’s largest nutrition study (and also the world’s largest Covid 19 study), where you can do your own personal experiments on chocolate (and much else).

Too Good to Be True?

Since the discoveries of ghrelin and leptin (and other hormones impacting hunger), scientists have had great fun designing various experiments, including:

  • Researchers in Denmark produced a paper suggesting that merely smelling dark chocolate can “increase satiety” (i.e. make you feel full) and decrease ghrelin levels. They also reported that the reduction in your ghrelin level was the same whether you ate, or merely smelled, the chocolate. Sadly the study didn’t show that you can double your feeling of satiety by first sniffing and then savouring your chocolate, although this is still the way we’d recommend enjoying your craft chocolate.
  • Another study, this time of US college students, revealed that describing the same 380 calorie milkshake as either “a 620-calorie “indulgent” shake” or a “140-calorie “sensible” shake” dramatically impacted how full participants felt, and how much ghrelin they produced. That is to say even though the two milkshakes were exactly the same, how full people felt, and how much their ghrelin levels declined, was driven by being told whether the items were low or high in calories and nutritional content. So even though these sadly there weren’t chocolate milkshakes, it does argue that you should luxuriate in the richness, the calories, and all the nutritional benefits of your chocolate as this will both psychologically and physiologically benefit you.

One of the major problems with both of these studies is their small sample size. The Danish study on smelling versus savouring chocolate had 12 subjects. And the milkshake study had 46. To be fair, it’s mainly the media reporting of these studies that have ‘hyped’ the results. For example the milkshake study conclusion reads “The effect of food consumption on ghrelin may be psychologically mediated, and mindset meaningfully affects physiological responses to food”, which I suspect most of us would agree with … once we’ve read this a couple of times.

Sample Size

Small sample sizes are, as any good scientist will testify, the Achilles’ heel of much research. For more on this, in particular with sugar, see an upcoming email where we’ll debunk the claims for coconut blossom sugar being healthier and a whole lot of other bunkum on ‘alternative sugars’ (see HERE for a teaser).

There are HUGE variations in how different people respond to different products depending on all sorts of personal, and environmental, factors (e.g., time of day, tiredness etc.). So it’s hard to rely on such small numbers.

What we really need are bigger studies. And more personalisation.

Personalised Nutrition

As in many other spheres ‘big data’ is trying to address these challenges, making waves not just in food but many aspects of health. For example, the covid 19 app launched by Professor Tim Spector and the ZOE team has hugely helped, and sped up, the understanding of covid by assembling millions of people to report regularly on their covid status and symptoms.

The ZOE team was originally set up to provide insights into “how your gut, blood sugar and blood fat respond to different foods” (including chocolate). The science is based on thousands of individual  studies (including 12,000 identical twins to understand the impact of DNA). And it’s highly personalised. For example, I took part in an early pilot a few years ago and amongst other insights, I was delighted to discover that consuming dark chocolate (in moderation, i.e. 5-6 squares at a time) doesn’t cause my blood sugar levels to ‘spike’, and definitely does satiate me.  On the less good side coffee (black or with milk) causes my blood sugar levels to spike.

For more on the ZOE study (and how to sign up), please see HERE.

And for those interested, yes, we are planning more ‘Craft Chocolate Conversation‘ sessions with Tim (register your interest HERE). Jonathan, one of Tim’s co-founders and ZOE’s CEO, has also done a podcast/YouTube interview with Tim and I. And Jonathan has a great interview podcast with Azeem Azhar explaining ZOE.


While you wait for your personalised nutrition plan, please don’t believe everything you read about chocolate (or any other food). Check out the sample sizes behind any studies whose results are “too good to be true”. 

And learn from the lessons of history. For the past 400+ years in Europe and 4,000+ years in South America, we’ve learnt that chocolate is delicious and filling. And it doesn’t need loads of sugar and additives to be delicious (in fact if sugar is the first ingredient listed on the label, we’d STRONGLY advise putting the bar back on the shelf).

To paraphrase the great Michael Pollan “eat craft chocolate, not too much, mostly dark”. And if you want great flavour, remember to check out the source of the beans, as without great beans (or grapes), you can’t make a great chocolate (or wine).

Below are a bunch of favourite bars from the team for you to experiment with. See if you find that smelling them really fills you up as much as savouring them. And remember, craft chocolate is nutritionally dense (and not full of sugar), so relax and delight in savouring them; keep thinking how filling they are…

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