The bulletproof diet: is it supported by science?

Dave Asprey created the Bulletproof diet based on his personal experiences and research into weight loss and wellness. Asprey is a Silicon Valley businessman and self-proclaimed bio-hacker whose Bulletproof diet and Bulletproof coffee have been featured in the New York Times, several podcasts, and news outlets. According to Asprey’s website, biohacking (also known as DIY biology) is “changing your environment from the inside-out so you have full control of your biology” and can "upgrade your life."

But what is the Bulletproof diet, and does it work as Asprey claims?

In a nutshell, the Bulletproof diet is a combination of intermittent fasting and a ketogenic diet, emphasizing proteins and fats while limiting carbohydrates. One of its primary tenets is that it ranks foods on a spectrum from “toxic” to “bulletproof,” with the bulletproof foods being the ones that supposedly help you lose weight. The Bulletproof diet claims to help you lose up to one pound a day. 

If scientific research has told us anything about dieting, there is no “best diet” that works for everyone. There are no shortcuts—if you eat fewer calories than your body uses per day, you will lose weight. Different dieting methods vary based on how restrictive they are, which nutrients they emphasize, etc. But the bottom line is the same—if you eat fewer calories than you burn, you will lose weight. 

The Bulletproof diet = ketogenic diet + intermittent fasting. Let’s talk about each of these dieting methods individually.

Ketogenic diet

The ketogenic, or “keto” diet, is a very low-carb diet that limits your carbohydrate intake to between 20–50 grams per day. You make up the rest of your calories with fats and proteins, with much more emphasis on fats than on proteins. (One popular type of keto diet is the Atkins diet). The theory behind this dieting technique is that when you limit your carbohydrate intake, you trigger your metabolism to enter a nutritional state called ketosis to help you burn fat (Abassi, 2018). During ketosis, your liver converts fats into ketones, which are then used as an energy source in place of carbohydrates, and your body switches into fat-burning mode (Masood, 2020). 

The upside of the ketogenic diet strategy is that some people on a ketogenic diet may feel less hungry, decreasing their overall calorie intake. This promotes weight loss without the burden of having to count calories (Abassi, 2018). At the start of a ketogenic diet, you may lose a lot of weight quickly, up to 10 lbs in two weeks or less. However, most of this weight loss is likely water weight, with the fat loss coming later (Masood, 2020). 

You may be wondering, with that much weight loss, why isn’t everyone adopting a ketogenic diet? Well, as you’ve heard over and over, there is no magic diet. In fact, there are several downsides to keto diets. 

Some people experience the “keto flu” with symptoms like nausea, vomiting, headache, fatigue, dizziness, and constipation. These symptoms usually only last a few weeks. Long-term consequences of keto diets can include fatty liver disease and kidney stones. Also, because you are eating more fats, the keto diet may raise your “bad” cholesterol levels—this may increase your risk of atherosclerosis and heart disease (Masood, 2020). 

There is also the issue of maintaining this diet for a long time. Restrictive diets like the keto diet and the Bulletproof diet are very hard for many people to stick to for the long haul. As expected, when you go off the diet, the weight comes back, leading to frustration and potentially an unhealthy relationship with food (Beuno, 2013). 

Intermittent fasting

The second arm of the Bulletproof diet is intermittent fasting, a dieting strategy where you eat and fast on a daily or weekly schedule. One of the reasons intermittent fasting is so popular is that you can adapt the fasting timing to your schedule. The program is flexible, and there are different ways to set up your feeding/fasting timings. 

• In the 5:2 method, you eat normally for five days and then fast for two. 

• Alternatively, you can do a “time-restricted” feeding, where you only eat during a “feeding window” like 8 am to 6 pm. 

• Some people prefer to fast one day, eat normally the next, and so on in an alternating day pattern. 

It is really up to you—since you are eating for short time intervals, you are taking in fewer calories without calorie counting. You don’t have any restrictions on what you eat, but rather on when you eat. 

Fortunately, there aren’t any health-related downsides to intermittent fasting. Some people may experience temporary side effects like fatigue, headaches, constipation, bad breath, difficulty concentrating, and irritability (Gardner, 2018). Unsurprisingly, data suggests intermittent fasting works for weight loss, but it is not necessarily any better than just reducing your daily calorie intake. However, decreasing your “feeding window” time may help some people consume fewer calories (Rynders 2019). 

Bulletproof diet

Knowing more about the Bulletproof diet components, it should not surprise you that you can lose weight using this dieting method. Just by switching to a keto diet, you are likely to lose weight, especially in the first few weeks—but know that this is mainly water weight and fat loss comes later. Combining keto with intermittent fasting makes it more likely that you are eating fewer calories than you were before starting the weight loss program. That by itself will help you lose weight. This diet is not without its issues, though.

While there’s a good chance you’ll lose weight on the Bulletproof diet (especially in the beginning), it comes with some serious downsides. 

Toxic foods

One of the main pillars of the bulletproof diet roadmap is that some foods are “toxic” while others will help you lose weight and are “bulletproof.” 

As part of this philosophy, the Bulletproof diet advocates removing all grains and gluten from your diet; even whole grains are considered harmful for you. Legumes, like beans and lentils, are also off-limits. However, whole grains and legumes contain fiber, which aids digestion and helps you feel fuller longer. Numerous studies have shown that diets rich in fiber can lower your cholesterol. The American Heart Association (AHA) recommends high fiber diets to decrease your risk of high cholesterol, atherosclerosis, heart disease, and diabetes (AHA, 2018).

Eliminating almost an entire food group makes this a very low-carb restricted diet, which is harder to follow long-term and leads to “falling off the wagon” and frustration (Bueno, 2013). 

According to the Bulletproof diet, other food groups considered “toxic” are most fruits and almost all dairy products. Fruits provide many nutrients, including fiber, and can even help with weight loss (Schroder, 2010). And while dairy products may cause problems for people who have milk allergies or sensitivities, the data does not support the belief that all dairy causes inflammation in everyone. Dairy products can also be a good source of protein, calcium, and vitamins (Bordoni, 2017). 

In creating its “bulletproof” food list, the Bulletproof diet recommends that you only consume organic or grass-fed meat and dairy products because they have more health benefits. There’s nothing wrong with going organic, but, this can get very expensive over time, creating yet another barrier for people to stay on this diet. (And, just for the record, studies show that non-organic products are just as healthy as organic ones) (Smith-Spangler, 2012).

Medium-chain triglycerides (MCT)

Medium-chain triglycerides (MCTs) are a type of saturated fat that comes from artificially processing coconut oil and palm oil. The Bulletproof diet claims that MCTs have specific fatty acids that power your brain and help you lose weight. They are more easily absorbed and broken down because of their chemical structure, helping you achieve nutritional ketosis faster; however, this effect only lasts about two weeks. Studies have not definitively shown that adding MCTs to a ketogenic diet may help with significant weight loss, and more research is needed to support these claims (Mumme, 2015). 

The Bulletproof diet emphasizes using MCT supplementation as a form of healthy fats. Their proprietary formula Bulletproof Brain Octane MCT is used to make Bulletproof Coffee and other things like salad dressings. There’s no proof behind Bulletproof’s claims about MCT’s safety and efficacy, though (Mumme, 2015). 

Proprietary products

You should be skeptical of any diet program that’s based on their own special foods or products for weight loss. The Bulletproof diet touts their own formulations of MCT oil supplements, like Bulletproof Brain Octane oil, Bulletproof Brain Octane soft gels, and FatWater (water mixed with Brain Octane MCT oil). Bulletproof coffee was a popular way to use these products—add Bulletproof Brain Octane MCT oil and two tablespoons of grass-fed ghee or grass-fed butter to your coffee, made from Bulletproof brand coffee beans. And it’s not cheap—about one quart of Bulletproof Brain Octane MCT oil costs almost $50.

Undervalues exercise

The Bulletproof diet claims that you should exercise infrequently, with only one brief, vigorous exercise session a week. However, the Physical Activity Guidelines for Americans put out by the U.S. Department of Health and Human Services (HHS) recommends the average adult workout regimen include at least 150–300 minutes of moderate-intensity physical activity (like brisk walking) per week along with strength training (HHS, 2018). 

Studies also show that adding exercise to dieting improves weight loss more than dieting alone, especially in the long run (Johns, 2014). Also, people who exercise regularly are more likely to keep the weight off (Swift, 2018). 

The short answer: The science does not support the weight-loss claims of the bulletproof plan, especially for long-term weight loss. 

Highly restrictive diets, like the bulletproof diet, may jump-start your weight loss, but they do not usually work to keep the weight off because it’s challenging to stay on a diet like this for a long time. The key to successful weight loss is finding something you can stick with long-term. 

Most nutritionists or dietitians recommend slow and steady weight loss, about 1–2 lbs per week—this is much slower than the one pound per day the Bulletproof diet claims (NIDDK, 2017). A successful diet encourages healthy lifestyle changes, like whole foods, more fruits and veggies, and increased physical activity—you want to be healthy and keep the weight off. Don’t fall for diet gimmicks that focus on proprietary products and supplements.

It’s definitely not recommended to follow Bulletproof’s exercise recommendations. Increasing your daily physical activity is essential, not only for losing weight but also for your overall health. In addition to helping you lose weight, exercise can help you keep that weight off, which is your ultimate goal. 

Remember, no diet plan works for everyone, and no magic food or oils will make you lose weight. Several variables affect how you lose weight, including age, gender, activity level, overall health, medications, etc. If you are unsure of what to do, get medical advice from your healthcare provider to develop healthy and realistic goals for your weight loss journey. 

Any diet plan you choose should be more about an ongoing lifestyle that you can maintain. This will allow you to achieve long-term changes in daily eating and exercise habits, translating to improvements in your health.

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Current version

February 26, 2021

Written by

Chimene Richa, MD

Fact checked by

Steve Silvestro, MD

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About the medical reviewer

Steve Silvestro, MD, Ro

Dr. Steve Silvestro is a board-certified pediatrician and Associate Director, Clinical Content & Education at Ro.