Asprey’s health claims for the coffee are certainly persuasive. The double shot of caffeine will speed your metabolism (studies have shown this) but the addition of fat (in the butter and coconut oil) slows the digestive process, preventing a sudden energy spike, which means the coffee ‘hit’ is gentler and lasts longer than it normally would.
Grass-fed butter (such as Kerrygold) is also supposedly rich in cancer-fighting antioxidants, good cholesterol and vitamin K2 (which plays a role in ‘decalcifying arteries’) as well as omega-3s, fatty acids and betacarotenes, all of which are good for the brain, stamina and immune system.
Adding coconut oil gives a boost of lauric acid (a fatty acid), which some believe to be good for the immune system, and a particular type of fat called ‘medium chain triglycerides’ (MCTs). It has been argued that these MCTs are metabolised directly in the liver, meaning that they are more likely to be burnt as fuel than stored as body fat.
However, one cup of butter coffee packs 400-500 calories — more than a bacon sandwich — and 50g of saturated fat, which brings you alarmingly close to your total daily allowance of 70g in just your first drink of the day.
As a result, many experts say it is hard to understand how this can possibly contribute to weight loss. Dietitian Dr Sarah Schenker says: ‘Ketosis is only triggered when the liver glycogen stores are depleted, so if you enjoyed a carb-heavy takeaway the night before, your morning cup of bullet coffee won’t be enough to make the switch.’
BY the same token, if you succumb to a baked potato at lunchtime or a couple of biscuits mid-afternoon, the low-carb magic will be lost and your butter coffee becomes no more healthy than buttered toast.
Although butter is very high in saturated fat, studies increasingly suggest that the link with heart disease is contentious. But there are concerns that too much butter (and some bullet coffee blends contain two tablespoons of the stuff) could increase cholesterol levels, raising your risk of heart disease.
Certainly, by drinking a high-fat, high-calorie drink for breakfast without making other changes to your diet or lifestyle, you are more likely to gain weight than lose it.
‘If you are trekking in Tibet you need concentrated calories because you are expending so much energy,’ says Dr Schenker, ‘But you can’t just transfer the drink to our more static Western environment and expect it to aid weight loss: it just won’t work.’
She suggests sticking to regular coffee without cream, butter or sugar — however rare it might be nowadays to ask for a simple, straightforward coffee with milk.