Bulletproof Coffee: The Butter-Coffee Trend, Who It's For, and What the Evidence Actually Shows

In 2004, Silicon Valley entrepreneur Dave Asprey arrived at a guesthouse in Tibet at high altitude, exhausted and cold. A local served him a cup of tea blended with yak butter. According to Asprey's own account, the effect on his energy and mental clarity was dramatic. He spent the following years working with nutritionists and food scientists to develop a version of the concept using coffee, eventually publishing the recipe in 2009 and launching the Bulletproof brand around it. The formula: brewed coffee blended with one to two tablespoons of grass-fed unsalted butter and one tablespoon of medium-chain triglyceride (MCT) oil. By the mid-2010s it had become one of the most-discussed dietary trends in the English-speaking world, enthusiastically promoted within the ketogenic and biohacking communities. A decade later, the evidence is clear enough to separate what the drink genuinely does from what it merely claims.

The Origins and the Brand

Asprey's company, Bulletproof 360, sells a proprietary range of products built around the core concept: Bulletproof coffee beans (marketed as "upgraded" and low in mycotoxins, a claim disputed by food scientists), Brain Octane C8 MCT oil (a refined MCT product), and Kerrygold-style grass-fed butter. The brand is worth distinguishing from the underlying recipe. You do not need Bulletproof-branded products to make bulletproof-style coffee. The core ingredients are any quality brewed coffee, grass-fed butter (the grass-fed designation is associated with higher conjugated linoleic acid content), and a standard MCT oil, available from multiple brands including NOW Sports, Sports Research, and Perfect Keto. The Bulletproof brand products cost significantly more than comparable alternatives.

The Claims and What the Evidence Shows

Bulletproof coffee's proponents claim it provides sustained energy without a blood sugar crash, suppresses hunger for several hours, enhances cognitive function, and improves fat burning. These claims deserve individual examination.

Sustained energy without blood sugar crash: this is one of the more defensible claims, with an important caveat. Consuming fat alongside or instead of carbohydrates does produce a more stable blood glucose profile after a meal. Fat is metabolised slowly, does not trigger significant insulin release, and does not produce the glycaemic spike-and-crash associated with high-carbohydrate breakfasts. If bulletproof coffee replaces a bowl of cereal or a pastry, the blood sugar effect is likely to be more stable. However, this is a property of fat in general, not of this specific combination.

Appetite suppression: MCT oil has documented effects on satiety. A 2003 study published in the American Journal of Clinical Nutrition found that MCTs increased satiety hormone release and reduced overall food intake at a subsequent meal compared to long-chain triglycerides. The fat content of bulletproof coffee (typically 25 to 40g depending on how much butter and MCT oil is used) is substantial enough to delay gastric emptying and suppress hunger meaningfully. For people who would otherwise eat breakfast, this effect is real. It is not, however, unique to the butter-coffee combination: the same fat calories from any source would produce similar satiety.

Cognitive enhancement: MCT oil raises blood ketone levels measurably, even in people who are not following a ketogenic diet. Ketones are an alternative fuel for the brain, and proponents argue that elevated ketone levels improve cognitive performance. The evidence here is more modest: some studies in people with mild cognitive impairment (particularly those with Alzheimer's-related decline) have found MCT supplementation beneficial, but studies in healthy adults are smaller and less conclusive. The caffeine in the coffee is, in controlled trials, a reliable cognitive enhancer. The specific contribution of the butter and MCT oil to mental clarity in healthy people is not clearly established in the literature.

Fat burning: MCTs are metabolised differently from long-chain fatty acids. They bypass the lymphatic system, go directly to the liver, and are preferentially converted to ketones rather than stored as fat. A 2001 study in Obesity Research found that MCT consumption over 27 days produced slightly greater fat loss than equivalent calories from olive oil in overweight men. The effect is real but modest and is only maintained in the context of an overall calorie deficit. Bulletproof coffee is not a fat-burning mechanism in isolation.

The LDL Cholesterol Question

This is the most important caution that mainstream coverage of bulletproof coffee often downplays. Butter is high in saturated fat (approximately 7g per tablespoon), and saturated fat is the primary dietary driver of LDL cholesterol elevation in most people. A 2020 randomised controlled trial published in the European Journal of Preventive Cardiology found that drinking coconut oil, a saturated fat with a similar fatty acid profile to butter, significantly raised LDL cholesterol compared to olive oil or unsaturated fat controls. Asprey's response has been that the type of saturated fat matters and that grass-fed butter specifically is beneficial, but this position is not supported by the weight of cardiovascular evidence.

For individuals with existing cardiovascular risk factors, elevated LDL, family history of heart disease, or who have been advised by a physician to reduce saturated fat, bulletproof coffee as described deserves genuine caution. The ketogenic community often dismisses LDL elevation as less relevant in the context of very-low-carbohydrate diets (a debate that remains active in cardiology), but this is a nuanced scientific argument, not a settled fact.

Calories: The Number People Often Overlook

A standard bulletproof coffee made with two tablespoons of butter (204 calories) and one tablespoon of MCT oil (130 calories) added to brewed coffee produces a drink containing approximately 230 to 350 calories in a minimal version, and up to 500 calories in a more generous preparation. This is equivalent to a substantial breakfast. Within a ketogenic dietary framework where total daily carbohydrate is limited to under 50g, these calories can fit into a dietary plan without promoting fat gain. Outside that framework, adding 350 to 500 calories to a regular diet is simply additional caloric intake.

The drink is sometimes described as a "fasting" tool, but at 350 or more calories, it breaks a caloric fast by any conventional definition. Its compatibility with intermittent fasting depends on which fasting goal is being pursued.

Who Bulletproof Coffee May Genuinely Suit

People following a well-formulated ketogenic diet (under 50g net carbohydrates per day) have the clearest rationale for bulletproof coffee. In that context, a high-fat, low-protein, zero-carbohydrate breakfast substitute that maintains ketosis, suppresses appetite, and provides energy from fat is consistent with the dietary framework. The MCT oil specifically supports ketone production, which is a meaningful benefit within that system.

People doing extended intermittent fasting (16:8, 18:6, or OMAD protocols) who find the fasting window difficult to maintain without eating may also benefit. Bulletproof coffee produces minimal insulin response compared to a carbohydrate-containing meal, and for fasting goals centred on insulin management or metabolic health rather than strict caloric abstinence, it may be a reasonable compromise. For those whose fasting goal is cellular autophagy, the fat content, particularly if it includes protein-adjacent signalling, is more problematic.

Athletes doing morning training in a fasted state sometimes use bulletproof coffee as a pre-workout energy source that avoids the gastric distress of a full meal. The fat provides sustained energy for low-intensity aerobic work, though it is less effective than carbohydrates for high-intensity performance.

Who It Probably Does Not Suit

People with cardiovascular risk factors or elevated LDL should discuss the saturated fat load with their doctor before adopting bulletproof coffee as a daily habit. People trying to lose weight who are not in a caloric deficit should be aware that adding 350 to 500 calories of fat to their day without removing equivalent calories elsewhere will not produce weight loss. People who are not following a low-carbohydrate diet and are adding bulletproof coffee on top of their regular breakfast are simply consuming more calories with no particular metabolic advantage.

A Simpler Alternative

For those drawn to the concept but wary of the saturated fat content, MCT oil alone in coffee is a lower-calorie and lower-saturated-fat version of the same approach. One tablespoon of MCT oil adds around 130 calories, raises ketones measurably, and has genuine satiety and energy-support evidence. Without the butter, the drink is also easier to prepare (no blending required, since MCT oil disperses more readily in liquid). This approach captures most of the evidence-based benefits without the cardiovascular cautions of daily high-dose butter consumption.

Related: Coffee and Intermittent Fasting: Does It Break Your Fast? | Coffee and Liver Health: The Research Explained