Super Human: The Bulletproof Plan to Age Backward and Maybe Even Live Forever. Dave Asprey

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      Until recently, we did not fully understand why fasting was so beneficial. Then in 2019, scientists at the Okinawa Institute of Science and Technology discovered that just fifty-eight hours of fasting dramatically increases levels of forty-four different metabolites, including thirty that were previously unrecognized.¹³ Among other beneficial functions, these metabolites—substances formed during chemical processes—boost antioxidant levels in the body. And as we know, antioxidants are important for fighting off aging free radicals. All of these benefits can be explained by the fact that fasting dramatically boosts autophagy,¹⁴ keeping your cells young and healthy.

      Fasting has profound effects, even at less than fifty-eight hours. Alternative day fasting, a form of intermittent fasting in which you eat every other day, helps prevent chronic disease and reduce triglyceride and low-density lipoprotein (LDL) cholesterol levels in as little as eight weeks.¹⁵ Intermittent fasting also increases your brain’s ability to grow and evolve by boosting neuronal plasticity (the brain’s ability to change throughout your life) and neurogenesis (the birth of new neurons).¹⁶ This can help ward off Alzheimer’s and cognitive decline.

      As you might expect, when I started experimenting with intermittent fasting ten years ago, I was often left feeling cranky and cold around lunchtime, before my eating window opened. This is because I had not yet developed the metabolic flexibility from teaching my body to efficiently burn carbohydrates or fat. Today I can effortlessly fast for twenty-four hours because my metabolism is younger and my blood sugar levels have stabilized. Thankfully, there are now well-understood ways to make intermittent fasting painless, which you’ll read about later.

      A BIG FAT LEAP OF FAITH

      So, when it comes to aging, grains are bad, sugar is bad, fried stuff is bad, and too much or too little protein is bad. What about fat? Can you eat too much of it? Sure. But we need fats for reproductive health, temperature regulation, brain function, and shock absorption. Fat helps build the outer lining of your cells, which protects them from damaging substances. It also makes up the bile acids you need to digest foods, and vitamins A, E, D, and K are fat soluble, meaning your body needs fat to absorb them. Additionally, several important hormones, including leptin, which helps you feel satiated, are made from saturated fat and cholesterol. Fat is also the basis for the lining of your nerves, called myelin, which allows electricity to flow efficiently between nerves and is essential for avoiding degenerative diseases like multiple sclerosis.

      Saturated fat in particular is so important that your body converts carbs to palmitate, a type of saturated fat, in a process called de novo lipogenesis. Without this ability, you’d die. That’s how critical saturated fat is. Your body then converts palmitate into other saturated and monounsaturated fats necessary for cell membranes, but it can’t make enough polyunsaturated omega-6 and omega-3 fats. That’s why you have to eat them. Yet the myth that eating fat and cholesterol will make you fat and give you heart disease still somehow persists. You read earlier that it’s your gut bacteria and not dietary cholesterol that creates plaques that build up in arteries. The evidence is in, and the fats you eat that contain cholesterol are not the enemy, as we’ve been told.

      When you eat enough of the right fats without excess carbs or protein, your body learns to efficiently burn fat for fuel. If you eat excess carbs or protein, your body burns those first. Normally, your body converts carbohydrates to make glucose, which your mitochondria use to produce energy. When you run out of carbohydrates, you start converting fat to glycerol for energy. The liver produces ketones as a by-product of this fat metabolism, and your mitochondria burn those ketones instead of glucose in a more efficient form of energy production. Ketosis is a state your body enters when you have a lot of ketones in your blood and are burning additional fat … or when you eat a special type of saturated fat that converts to ketones in your body. More on that later.

      One last time: Your body requires fats for you to perform your best and live as long as possible. You just have to know which fats serve what purpose. Some fats you eat are building blocks for your body, and some are better used as fuel. Getting the mix right matters. But have you ever heard nutrition “experts” say exactly which of the many saturated (or other) fats to avoid? The typical buckets you hear (“plant based,” “animal fats,” “saturated,” “polyunsaturated”) are not very specific. Is it possible that the heated industrial polyunsaturated fat in French fries has a different effect on your biology than avocado oil, or that the fat in industrially-raised animals is different from the fat in an egg yolk or pastured beef? You bet it is.

      Researchers in Australia have measured how different cells elegantly use each type of fat you eat. You can make sure your brain has the type of fuel it runs best on and that your body fat doesn’t create extra inflammation and make you old. Eating the right fats could add productive years to your life, which is why it’s worth a page or two of your time to dig a little deeper into details of how your body uses fats.

      Scientists describe cell membranes as “the margin between life and death for individual cells.”¹⁷ These membranes are made of tiny droplets of fat. About 5 percent of your genes contain instructions telling your cells how to make the thousands of types of fat your body needs to survive. We now know so much about what each different type of fat does that French researchers have proposed the notion that “saturated fats should no longer be considered as a single group in terms of structure, metabolism, and functions.”¹⁸ In other words, we have grouped together a very diverse array of fats under one reductive and often misleading label. When your doctor tells you to eat less saturated fat, your response should be “Which one(s) do you mean?”

      I’ve had the opportunity to interview lots of fat experts (or experts on fat), and most of us use an analogy from nutritionist and early trans fat researcher Mary Enig, PhD, who popularized two basic ways of thinking about the fat you eat. The first is to look at how long a fat molecule is. There are short-chain, medium-chain, and long-chain fats. As a general rule, the shorter the saturated fat, the more anti-inflammatory it is. For instance, butyric acid, which is anti-inflammatory, has only six molecules, while other types of fat may have twenty or more.

      Some fats are easy to damage no matter how long they are. So the second way to understand your fat is to assess its stability. Oxygen drives very strong chemical reactions that damage fats through oxidation. Oxidized (damaged) fats cause you to age more quickly by creating inflammation in the body and building less effective cell membranes. When your body has no choice but to incorporate oxidized fats into cell membranes, those cells create excess free radicals that make you an average human, not super.

      Your cells use saturated fats, which are the most stable of the fats, to make about 45 percent of the cell membranes in the brain and liver, and about 35 percent in heart and muscle cells.¹⁹ Yes, saturated fat is the dominant fat in your brain, so don’t demonize it! Energy-producing cells will hold their level of saturated fat at about this level no matter what type of fat you eat. The only type of tissue that meaningfully changes its composition of saturated fat is adipose tissue—aka your muffin top. When you eat more saturated fats, the cells in adipose tissue will change their makeup to contain more saturated fat and less unstable fats without changing in size. This is fantastic, as stable fats make for fewer free radicals.

      Think of saturated fat as the stable waxy bricks building the “walls” for your cells. The problem is that your cell membranes have to flex in order to make energy and receive chemical signals, and those nice stable saturated fat “bricks” don’t bend. So while it’s fine to go ahead and eat butter and other forms of saturated fat, it’s also important to eat other types of fats. And those include the next most stable group of fats, monounsaturated fats. These fats—found in food sources like olive oil, avocados, and some nuts—are more flexible than saturated fats. You can think of them as the gel-like “mortar” that supports your saturated fat bricks in the cell wall. Your cell membranes are made up of about 20 percent monounsaturated fat.

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