Book review: "The bulletproof diet" by Dave Asprey

Core principles of the bulletproof diet

At its foundation, the Bulletproof Diet is a high-fat, moderate-protein, low-carbohydrate approach with several distinguishing characteristics:

• Macronutrient Breakdown: 50-70% calories from fat, 20% from protein, and 5-30% from carbohydrates
• Food Quality: Emphasizes grass-fed meats, wild-caught seafood, organic vegetables, and healthy fats while eliminating processed foods
• Toxin Avoidance: Focuses on minimizing exposure to “anti-nutrients” including lectins, phytates, oxalates, mycotoxins, and histamines
• Intermittent Fasting: Restricts eating to a 6-hour window daily, often skipping breakfast in favor of Bulletproof Coffee

The diet’s signature element is Bulletproof Coffee—a blend of specific coffee beans, grass-fed butter, and MCT oil that Asprey discovered after drinking yak-butter tea in Tibet. This concoction supposedly provides sustained energy without breaking a fast, supporting mental clarity and focus throughout the morning.

Additionally, the diet categorizes foods into green (“bulletproof,” eat freely), yellow (“suspect,” consume with caution), and red (“toxic,” avoid) zones. The plan also incorporates a cyclical approach to ketosis with a weekly “refeed” day allowing up to 300 grams of carbohydrates.

The bulletproof coffee experience

The most recognizable element of the Bulletproof Diet is undoubtedly the coffee. A standard cup contains approximately 230-250 calories and 25 grams of fat with zero carbohydrates, made from three core components: high-quality coffee beans, grass-fed butter or ghee, and medium-chain triglyceride (MCT) oil.

Asprey insists on using low-toxin coffee beans supposedly free of mycotoxins (fungal compounds). The butter must be unsalted and grass-fed, theoretically higher in omega-3 fatty acids and fat-soluble vitamins than conventional butter. Meanwhile, MCT oil—derived primarily from coconut oil—provides rapidly digested fats that convert quickly to energy.

Many users report that unlike regular coffee’s jittery stimulation, this high-fat version provides a smoother energy curve. By the second week of implementation, many experience what enthusiasts describe—sustained morning focus without the typical caffeine crash. Research suggests the fats from butter slow caffeine absorption, delivering steadier energy.

Regarding satiety, a randomized crossover trial found participants reported greater fullness and lower perceived prospective food consumption after drinking Bulletproof Coffee compared to black coffee. This effect persisted approximately three hours post-consumption, making intermittent fasting considerably easier for many practitioners.

The energy boost from Bulletproof Coffee appears to come from two primary mechanisms. First, caffeine itself stimulates ketone production in a dose-dependent manner—higher caffeine intake correlates with higher ketone levels. In one study, caffeine increased ketone production by 88-116%. Secondly, MCT oil rapidly converts to ketones in the liver. These ketones serve as alternative brain fuel, potentially improving mental clarity when carbohydrates are restricted.

However, contrary to some marketing claims, a controlled study found no significant difference in cognitive performance between Bulletproof Coffee and black coffee on standardized tests. The primary benefits appear to be metabolic rather than cognitive.

Weight loss and body composition results

One of the most intriguing aspects of the Bulletproof Diet is its counterintuitive approach to weight loss. Despite consuming approximately 4,000 calories daily—including copious amounts of butter—many followers experience steady weight loss without counting calories or restricting portions.

More significantly, body composition improvements often exceed what the scale shows. Research published in the American Heart Association’s journal found that low-carb, high-fat diets reduced dangerous fat deposits around organs even when weight loss was minimal. Many practitioners confirm reductions in waist circumference consistent with decreased visceral fat.

Notably, these improvements occur despite dramatically higher fat consumption than conventional dietary wisdom recommends. As Asprey argues, “saturated fat is a stable fat that your body needs to create proper cell membranes and hormones.”

The most immediate effect many report is on hunger patterns. After an initial adjustment period of approximately one week, cravings for carbohydrates and sugar often diminish substantially. This aligns with research showing that polyunsaturated fats increase levels of peptide YY (PYY)—a satiety hormone that suppresses appetite.

The diet’s fat-burning mechanism works through ketosis, where the body uses fat reserves for energy instead of carbohydrates. Consequently, energy levels remain remarkably stable throughout the day for many followers, without the afternoon crashes previously experienced on higher-carb diets.

Scientific scrutiny: Strengths and weaknesses

Strengths:

• Fat Rehabilitation: Asprey successfully demystifies the fear of fats, especially saturated fats, which aligns with newer scientific understanding
• Satiety and Energy: The high-fat approach does provide sustained energy and reduced hunger for many practitioners
• Processed Food Reduction: Eliminating processed foods and focusing on whole, quality ingredients is scientifically sound
• Inflammation Focus: The emphasis on reducing inflammation in the body is scientifically grounded and beneficial

Weaknesses:

• Mycotoxin Claims: Many claims, especially those about mycotoxins in food, aren’t supported by solid scientific evidence. Studies indicate mycotoxins exist in coffee beans, with one showing 91.7% of green coffee beans contained mold. Nevertheless, modern processing methods significantly reduce these compounds, with roasting decreasing ochratoxin A levels by 69-96%. Furthermore, mycotoxin levels in commercial coffee typically fall well below safety limits established by regulatory authorities.
• Antinutrient Exaggeration: The Bulletproof approach targets antinutrients—compounds that theoretically block nutrient absorption, including lectins in legumes and grains, phytates in grains, and oxalates in leafy greens. However, research indicates these compounds exist but have limited practical significance. Harvard’s Nutrition Source notes “the health benefits of eating these foods outweigh any potential negative nutritional effects.” Traditional preparation methods like soaking, sprouting, and cooking substantially reduce antinutrient content.
• Selective Evidence: Asprey often cites studies on mice without clearly stating they weren’t conducted on human subjects
• Extreme Restrictiveness: The regimen is extremely restrictive and difficult to maintain for the average person
• Commercial Interests: The book promotes Asprey’s own products, creating a potential conflict of interest

Expert and reader opinions

Expert opinions on the “Bulletproof Diet” are largely critical. Red Pen Reviews, a platform that rates nutrition books based on scientific accuracy, gave the book an overall score of just 49%. A particularly low score (34%) was assigned for scientific accuracy, while reference accuracy received a somewhat better rating (70%).

Experts particularly criticize Asprey’s claims about mycotoxins in coffee and their impact on cognitive function, for which there isn’t sufficient scientific evidence. Also, many nutritionists dispute the extremely high fat intake that Asprey advocates.

However, some experts acknowledge that certain elements of the diet may be beneficial, such as reducing sugar and processed food intake and emphasizing quality protein sources.

Reader opinions are divided, but several common themes emerge. Many praise the energizing effect of “Bulletproof Coffee” and the feeling of satiety it provides. One Goodreads reader writes: “I didn’t read this because I wanted to lose weight. Rather, I was interested in nutrition, and Bulletproof Coffee really gave me energy without feeling hungry throughout the morning.”

Other readers appreciate Asprey’s emphasis on food quality and reducing inflammation. However, many point out that the regimen is difficult to maintain long-term due to its restrictiveness and cost (organic food, special oils, and supplements can be expensive).

Interestingly, even those who criticize the scientific foundation of the book often admit they experienced positive results by applying at least some of the advice.

Practical considerations: Cost and sustainability

Following the diet strictly requires significant financial investment. The Bulletproof brand MCT oil costs nearly $50 for a quart, while specialty supplements like Brain Octane soft gels add additional expenses. Even the recommended grass-fed meat and organic produce come at premium prices.

Throughout practical implementation, many find budget alternatives that Asprey himself acknowledges. Kerrygold butter sells for under $3 at stores like Trader Joe’s versus $4 for some specialty brands, and generic MCT oil costs significantly less than Bulletproof-branded versions.

The diet’s restrictiveness presents another challenge. The list of “kryptonite” foods to avoid is so extensive that many find their menu becomes too limited and socially impractical. This makes long-term adherence difficult for many people.

A balanced assessment

“The Bulletproof Diet” offers some valuable insights and practical advice but requires critical reading. Asprey has a talent for presenting complex topics in an accessible way and offers an intriguing perspective on optimizing nutrition for improved cognitive function and energy.

The best approach is probably selective – taking useful elements like reducing processed foods, experimenting with intermittent fasting (which Asprey advocates through skipping breakfast), and perhaps trying Bulletproof Coffee, but maintaining healthy skepticism toward extreme claims and very restrictive recommendations.

The book definitely isn’t for everyone, but for those willing to filter scientifically-based advice from exaggerations, it can offer interesting ideas for optimizing nutrition and energy. Just remember that, as with most diet books, it’s wise to consult with a healthcare professional before making significant dietary changes.

In the landscape of nutrition literature, “The Bulletproof Diet” represents an interesting case study in how personal experimentation, scientific research, and entrepreneurial marketing intersect. While not all of Asprey’s claims stand up to rigorous scientific scrutiny, his emphasis on food quality, reduced processing, and mindful eating contains valuable wisdom that transcends the more controversial aspects of his approach.