When people think of fasting, the image that often comes to mind is a skinny guy wearing a simple robe, sitting cross-legged in a monastery on a mountaintop. It has a decidedly spiritual context, in which the cleansing of the body is connected to the cleansing of the soul. In such a context, fasting is not connected to “real life,” in which you must go to work, get the kids off to school, clean the house, and complete all the mundane tasks we do every day.
In this book, we look at fasting differently. Responsible, smart fasting is meant for everyday life. It plays an integral role in your daily health and well-being, and therefore you need to know as much as you can about it. I believe fasting is nature’s reset button. There are many different ways to practice it, from daily intermittent fasting to extended water fasts—the key is to follow a schedule that keeps you within your hormetic zone, as we’ve discussed. Think of fasting like using a chainsaw. If you take the time to read the user manual before using it, you’ll see great results with this powerful tool. But if you skip the manual and try to use a chainsaw without any knowledge, you could easily hurt yourself. The tool is important, but how it’s wielded is just as crucial.
As you begin your 30-Day Metabolic Freedom Reset, I’ll guide you through IF protocols, starting with 12-hour fasts to build that muscle. We’ll gradually work our way to longer fasts, ensuring that you stay within your hormetic zone for optimal success. I understand that the idea of fasting, especially if you’ve never tried it before, may seem as daunting as holding your breath for five minutes. However, the way you’ll be practicing it will feel manageable, because you’ve already made the effort to strengthen your metabolic machinery.
In this chapter I’ll share the latest research on the benefits of fasting, which include lowering blood pressure, digestive health, brain health, and metabolism efficiency.
Back in 2014, I began researching the benefits of fasting. I was so excited to learn about this ancient healing tool that I immediately applied it to my schedule and experienced incredible results. I remember posting on my Facebook page about intermittent fasting, and I received so many concerned messages: “Ben, you are starving yourself. You are encouraging an eating disorder. You are going to wreck your metabolism.” I didn’t expect so much pushback! Back then the research was more limited, but now we have plenty of evidence showing how effective fasting can be. Fasting has even become one of the top search terms on Google.
One of the most comprehensive and highlighted studies ever conducted on the subject was published in The New England Journal of Medicine in December 2019. The authors reviewed more than 85 studies and suggested that IF should be used as the first line of treatment for diabetes, obesity, cancer, neurodegenerative brain conditions, and cardiovascular disease. The study examined an 18:6 IF method, which involves fasting for 18 hours each day followed by a 6-hour eating window. The study also revealed that IF has anti-aging benefits. This meta-analysis highlighted several key cellular healing benefits, including:
In terms of what we’re covering in this book, fasting will achieve four key benefits when it comes to restoring your metabolism:
Let’s take a closer look at each of these.
An estimated 103 million American adults have high blood pressure, according to recent statistics from the American Heart Association.1 That’s nearly half of all adults in the United States. The death rate from high blood pressure increased by nearly 11 percent in the United States between 2005 and 2015, and the actual number of deaths rose by almost 38 percent—up to nearly 79,000 by 2015, according to the statistics.2 “Worldwide, high blood pressure affects nearly a third of the adult population and is the most common cause of cardiovascular disease-related deaths,” said Paul Muntner, a professor and vice chair in the Department of Epidemiology at the University of Alabama at Birmingham.
According to the National Kidney Foundation and American Heart Association, high blood pressure cannot be cured, but it can be managed with medication. Is this true?
Throughout the 20th century, scientists noticed that when they took away food from patients with high blood pressure, their blood pressure levels would begin to drop. As the days passed, the pressure continued dropping until it eventually reached normal levels and flattened out. This was seen in a 1915 study of prolonged fasting from the Carnegie Institution, where patients underwent prolonged fasting for varying lengths of time, with some fasting for as long as 31 days.3
In the 1990s, Alan Goldhamer began to study the effects of fasting on a large group of individuals. Goldhamer runs the TrueNorth Health Center in Northern California, the largest medically supervised water-only fasting clinic. They looked at 174 of Goldhamer’s patients who came to TrueNorth with high blood pressure. They fasted on average for a week and a half on nothing but water and found that 154 (nearly 9 out of 10) normalized their blood pressure.4
Goldhamer and his colleagues submitted his groundbreaking findings to 30 journals, and they were rejected each time. Why would the medical community be interested in a healing tool that is free? There are billions of dollars to be lost from Big Pharma and Big Food if people catch on to the healing benefits of fasting.
A fun fact is that airline pilots visit Goldhamer’s TrueNorth clinic once a year to perform a 10-day water fast, so they can keep their blood pressure optimal, which is required to fly an airplane. If you’re concerned that I might ask you to go without food for days, don’t worry. The 30-Day Metabolic Freedom Reset is designed to help you achieve similar results with shorter fasting schedules. Think of it like tuning a car engine—you don’t need to overhaul the entire engine to improve performance; sometimes, just removing a few blockages can make it run smoothly. Similarly, by allowing your metabolism to function more efficiently and eliminating any interference, you’ll see the benefits without needing to endure extended fasts.
We usually think of food as giving us energy, but digesting the food we eat actually requires energy, as we discussed in Chapter 2. After a heavy meal, an estimated 65 percent of the body’s energy must be directed to the digestive organs. Chewing food and allowing the body to take macronutrients and assimilate them into micronutrients for distribution is a big task. During fasting, we rest our system from the constant onslaught of food and redirect our energy toward healing and recuperation. Our body can detox, repair cells, and eliminate foreign toxins and natural metabolic wastes.
Imagine a corporate employee named Jennifer who works 9:00 A.M. to 5:00 P.M. each day, putting in a full day of work. She clocks out of her job after a long day and walks to her car. As she approaches her vehicle, thinking about going home to rest and recover, she receives a phone call from her boss asking her to return to the office to work on an important project for the next five hours. Reluctantly, she goes back and puts in the extra work. It is now 10:00 P.M., and Jennifer is exhausted and ready to go home and rest. As she approaches her car again, she receives another phone call from her boss asking her to come back to the office to work on another project.
Imagine this happening to Jennifer for days, and even weeks, on end—she would begin to lose her ability to function. This is exactly what you’re doing to your digestive system when you’re not practicing IF. From the perspective of the gut, you’re not giving it the time it needs to rest in between meals.
After every meal, there is a little bit of endotoxemia (meaning the presence of endotoxins in the blood). Endotoxins are toxic substances, primarily made up of lipopolysaccharides (LPS), that are found in the outer membrane of certain bacteria in the gut. After eating a meal, these endotoxins can be released into the bloodstream if the gut barrier is compromised. This release can trigger an inflammatory response in the body, as the immune system reacts to what it perceives as a threat. Over time, repeated exposure to endotoxins can contribute to chronic inflammation and various metabolic disorders. It can vary by the types of foods and fats that you’re eating, and it can be worsened if you have a leaky gut. When you don’t eat, you reduce that endotoxemia, so you’re allowing the body to do its cleanup work to reduce inflammation and rebalance itself.
If you look historically at the number of meals that people ate 50 years ago compared to now, it used to be only three meals a day, and now it’s five or six meals per day. If this is the case with you, you’re not giving your body enough time for your blood sugar and insulin levels to drop, and the internal balance that improves your sensitivity to insulin can’t occur. When you’re eating too many meals, you’re not allowing that rest period that’s necessary for the body to be able to hit the reset button in between. We were not meant to live with a continuous influx of calories!
One meal can create an energy expenditure from the body for up to 72 hours, and that can take 70 to 80 percent of your energy levels. Think about that. I’m talking about the Standard American Diet, which is indeed SAD. We are overwhelming the digestive system, and it cannot keep up with the demand.
Fasting gives your digestive system a break, so it can use its resources for healing. I have seen this work well for the following digestive symptoms:
My client Patricia had been battling fatigue and brain fog for years. Despite trying various extreme diets, many of which encouraged frequent snacking between meals, she found herself feeling worse rather than better. Her energy levels were consistently low, her mind felt clouded, and she struggled with persistent digestive issues, particularly acid reflux. It seemed that no matter what she tried, nothing could shake the constant feeling of exhaustion and mental sluggishness.
When Patricia learned about fasting and we began to slowly build up her fasting muscle, everything changed. By gradually extending the time between meals, we allowed her metabolism to reset and function more efficiently. Patricia now reports having the energy of a teenager, with her brain firing on all cylinders. Her once-debilitating brain fog has lifted, and her digestive issues, including the persistent acid reflux, have completely disappeared. This is why I call fasting nature’s reset button!
Stem cells are special human cells that can develop into many different cell types, ranging from brain cells to muscle cells. In some cases, they can also fix damaged tissues. You might say that stem cells are the body’s ubiquitous, all-purpose cells from which all other cells with specialized functions are generated.
As you get older, your intestinal stem cells begin to lose their ability to regenerate. Because these stem cells are the source for all new intestinal cells, this decline can make it more difficult for an aging person to recover from gastrointestinal infections or other conditions that affect the intestine.
According to research from MIT biologists, this age-related loss of stem cell function could be reversed by a 24-hour fast.5 The researchers found that fasting dramatically improves stem cells’ ability to regenerate, in both aged and young mice.
“Fasting has many effects in the intestine, which include boosting regeneration as well as potential uses in any type of ailment that impinges on the intestine, such as infections or cancers,” said Omer Yilmaz, an MIT assistant professor of biology, a member of the Koch Institute for Integrative Cancer Research, and one of the senior authors of the study.
“This study provided evidence that fasting induces a metabolic switch in the intestinal stem cells, from utilizing carbohydrates to burning fat,” added David Sabatini, an MIT professor of biology, member of the Whitehead Institute for Biomedical Research and the Koch Institute, and also a senior author of the paper. “Interestingly, switching these cells to fatty acid oxidation enhanced their function significantly.”6
IF may also restore microbe diversity in the gut, increase tolerance against “bad” gut microbes, and restore the integrity of the intestinal epithelium.
A study published in the Scandinavian Journal of Immunology found that IF (this time, alternate-day fasting for 12 weeks) helped Salmonella-infected mice clear the pathogenic bacteria more quickly through a heightened immune response.7 Another study published in the journal Cell Metabolism found that every other day fasting alters the gut microbiome composition to promote an increase in the number of mitochondria in the fat tissue of mice.8
A study published in Frontiers in Microbiology in 2022 explored the impact of IF on gut microbial diversity and its associated effects on body weight and lipid profiles. The research involved 45 participants (14 women and 31 men) and analyzed blood and fecal samples collected before and after the fasting period. The study found that IF led to significant improvements in body weight and blood lipid profiles. Specifically, participants experienced an increase in high-density lipoprotein (HDL, the “good” cholesterol) and a decrease in total cholesterol, triglycerides, and low-density lipoprotein (LDL) levels. These changes were linked to favorable shifts in gut microbiota, including an increase in beneficial bacteria like lactobacillus and Bifidobacterium and a decrease in pathogenic bacteria.9
The (digestive) nervous system is also involved in about 30 neurotransmitters. It is estimated that 90 percent of the feel-good chemical serotonin is created in the gut. We just made the case for how fasting fixes the gut, now let’s make the case for fasting for the brain.
If there’s anything going on in your gut, signals are sent to your brain. This can cause unexpected symptoms and conditions, such as:
If there’s anything going on in the brain (like stress), it can cause symptoms in your gut, such as:
Brain-derived neurotrophic factor (BDNF) is like a brain fertilizer. It grows neurons and strengthens synaptic connectivity. When we are in a fasted state or high level of physical activity, we start producing more BDNF. It helps neurons grow and branch out toward each other, making it easier for them to communicate. This decreases the synaptic activity I mentioned earlier, which is very powerful. If we are decreasing the overall synaptic activity (the amount of communication going from neuron to neuron) but increasing the connectivity, we are increasing the potency of how that activity is communicated.
Imagine you have two people trying to communicate using a string-and-cup telephone, but the string is frayed and full of knots. The message gets distorted, and only a fraction of it makes it through. When you’re not fasting, your neurons are like those people struggling to communicate across that tangled, fraying string. However, during fasting, your neural connections become like a clear, strong fiber-optic cable—messages travel smoothly and efficiently. With a higher percentage of energy flowing through a well-maintained, uninterrupted connection, your neurons can communicate effectively, ensuring that the signals are transmitted clearly and without loss.
BDNF not only grows neurons but also grows the connection between them. It has antidepressant activity, which explains why when you’re fasting and after exercising you feel pretty damn good. The combination of BDNF and the decreased activity within the brain ends up being very powerful.
IF results in increased production of BDNF, which increases the resistance of neurons in the brain to dysfunction and degeneration in animal models of neurodegenerative disorders. BDNF signaling may also mediate beneficial effects of IF on glucose regulation and cardiovascular function.10
Many people are searching for ways to speed up their metabolism, but I doubt they want to shorten their lives in the process. Yet in the animal kingdom, the rate of living theory postulates that the faster an organism’s metabolism, the shorter its lifespan. First proposed by Max Rubner in 1908, the theory was based on his observation that smaller animals had faster metabolisms and shorter lifespans compared to larger animals with slower metabolisms.
In the world of longevity, nothing extends lifespan more than caloric restriction. It’s true that restricting your calories extends your lifespan, but you do this at the cost of your metabolism. Caloric restriction studies show positive outcomes for longevity in terms of reduction in blood glucose and insulin levels, sirtuin activation, and others, but it also creates a new set of problems: The metabolism and body go into starvation mode. Studies show that the immune system gets weakened, organs shrink, the thyroid slows down, and hormone imbalances occur (plus the participants in caloric restriction studies are miserable and cold all the time).11, 12
Won’t the body go into starvation mode when you practice IF? No! A recent study shows a 13 percent increase in metabolism efficiency after four days of fasting. The human body knows what to do. When we go through a period without food, incredible processes start in the human body. There is no slowdown in metabolism. It’s the complete opposite! The body starts to go into “survival mode” not “starvation mode.” The body wants us to find our next meal so that we can stay alive, so it raises counter-regulatory hormones (hormones that run counter to insulin). When we don’t eat food, insulin levels drop, and we raise these counter-regulatory hormones, which include catecholamines, cortisol, glucagon, and growth hormone. This is our body’s way of pumping us full of energy and focus so we can hunt for our next meal.
One of the key differences between caloric restriction and intermittent fasting is their impact on metabolism. When you simply restrict calories by eating less but continue to eat throughout the day, your metabolism tends to adapt and become less efficient. In contrast, with intermittent fasting, even if you’re in a calorie deficit, your metabolism doesn’t slow down. Instead, it becomes more optimized due to the influence of counter-regulatory hormones.
These hormones are why our metabolism efficiency increases with fasting. Adrenaline levels are increased so that we have plenty of energy to go get more food. For example, 48 hours of fasting produces a 3.6 percent increase in metabolic rate, not the so-called “metabolic shutdown.” In response to a four-day fast, resting energy expenditure increased up to 14 percent. Rather than slowing the metabolism, the body actually made it more efficient.13
There are three key metabolically active tissues inside your body:
Ancient healing strategies such as ketosis and fasting enhance all three of these important metabolically active tissues. Let’s dive into all three.
Adipose tissue is composed of fat cells, but there’s a big difference between white adipose tissue (WAT) and brown adipose tissue (BAT). White fat cells store energy in the form of a single large, oily droplet. They are otherwise relatively inert. In contrast, brown fat cells contain many smaller droplets as well as mitochondria. These organelles can burn up the droplets to generate heat. Humans are mammals, and unlike reptiles we generate our own internal heat. When the body is in a cold environment, these brown fat cells become activated and literally generate heat through chemical reactions that use the oily droplets for fuel. This helps us maintain our standard operating temperature, which for most people is 98.6 degrees Fahrenheit.
Babies have BAT, presumably because they cannot yet shiver when cold, so their warmth must rely more on burning brown fat. It was long assumed that BAT disappeared in adults. However, in 2009 three different groups independently published papers in the New England Journal of Medicine revealing their discoveries of active brown fat cells in healthy adults. Scientists have since been trying to figure out how to study brown fat more easily and in greater detail.
Research suggests that BAT has many more benefits than WAT, mostly due to its ability to burn more energy (calories) to be used for body heat.14, 15 During this process, your body’s internal temperature increases and helps reduce other fat deposits made of WAT, the type many of us need to decrease. Certain studies have even shown that brown fat can burn up to five times more calories than other types of body fat!16
Interestingly, because cold conditions activate brown fat, our ancestors—even those a few generations back—may have benefited from BAT’s fat-burning capability because they lacked central heat. Studies have shown that people exposed to cold indoor temperatures—not super cold, just a brisk 63 degrees Fahrenheit—burn more calories from fat than people in a warmer environment.
If you want to break free from weight-loss resistance, you need to make more brown fat. The most effective way to do this is to use ketosis and fasting, along with the cutting-edge biohacks I’ve included later in the book—your keys to metabolic freedom.
Muscle is the next metabolically active tissue inside your body that we want to prioritize. I’m not suggesting you have to become a bodybuilder, but lean muscle mass protects your metabolism in numerous ways. Muscle is mitochondrial dense, because it requires a large amount of energy to function. This is provided primarily by mitochondria in cells that consume a lot of energy.
Muscle mass helps to balance your blood sugar and insulin levels. We already discussed why high levels of blood sugar and insulin cause inflammation and weight gain—the more muscle mass you have, the more insulin sensitive you become. Think of your muscle as a sponge that mops up excess glucose out of your bloodstream, so insulin doesn’t have to work as hard. This means you can enjoy yourself at the wedding or event, and your body will know what to do with the excess sugar.
When I owned my CrossFit gym back in 2015, I used to hold seminars on fasting for the members. I recall that many of them were hesitant to try fasting because they feared it would undo their hard-earned gains from working out. However, fasting actually stimulates the production of human growth hormone (HGH), which not only prevents muscle loss but also enhances your ability to build lean muscle. Far from diminishing their progress, fasting can help athletes improve their muscle development and overall fitness.
Your gut microbiome plays a role in your metabolism, because if you’re consuming 1,500 calories per day, but you only absorb 900 calories, the excess will enter your bloodstream, creating an inflammatory response. The gut microbiome plays a crucial role in regulating metabolism, influencing everything from nutrient absorption to energy balance. The diverse community of microorganisms in the gut helps break down complex carbohydrates and fibers into short-chain fatty acids (SCFAs) like butyrate, acetate, and propionate. These SCFAs not only provide energy to the cells lining the gut but also play a key role in signaling pathways that regulate fat storage, insulin sensitivity, and inflammation. By modulating these processes, the gut microbiome can directly impact metabolic health, contributing to conditions like obesity, diabetes, and cardiovascular disease when its balance is disrupted.17, 18
The gut microbiome interacts with various hormones and metabolites that influence hunger and satiety, such as ghrelin and leptin. A healthy gut microbiome supports the proper function of these hormones, helping to regulate appetite and prevent overeating. Dysbiosis, or an imbalance in the gut microbiome, can lead to impaired signaling and contribute to metabolic disorders like insulin resistance and metabolic syndrome. Therefore, maintaining a healthy gut microbiome is essential for optimal metabolic function and overall health.19
Fasting is one of the fastest ways to repair the gut microbiome. Combine this with a diet rich in SCFAs, which is included in your 30-Day Metabolic Freedom Reset, and you’ve got yourself the perfect recipe. This again is because fasting repairs leaky gut, allowing you to digest important vitamins and minerals for metabolic function.
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You now know the extraordinary benefits that fasting has on your metabolic health, as well as its potential for treating various diseases. In the next chapter we’ll look at the foods that best support your metabolism when you do break that fast.