Ketosis gets credit for a lot of health benefits: sustainable fat loss, better energy, sharper cognition, the list goes on. But here’s the thing — if you’re not fat adapted, you won’t realize the full potential of these benefits. What’s the difference? Allow me to explain.
Most people have relied on carbs for brain fuel and quick energy their entire lives. Their bodies are efficient at it. On the other hand, if you’ve never relied much on fat, your body may not be very good at it — the old adage “use it or lose it” applies here. Your first few weeks in ketosis are much like your first few weeks back in the gym: You may remember how to bench press, but you’re not going to break your personal record.
As you stick to your ketogenic diet, you will adapt to utilizing fat over the course of several weeks to months. You’re practicing and improving your ability to break down fat (from both diet and body) into fatty acids, and then convert those fatty acids into ketones for energy.
Here’s another example to illustrate the difference between ketosis and fat adaptation. Let’s say Bobby eats a Standard American Diet — high in sugar and omega 6, low in fruits and veggies. Bobby sees an ad for ketones in pill form, promising weight loss. He buys a bottle, takes a few pills, his blood ketones rise, and bam! He’s in ketosis. Just one problem: Bobby isn’t fat adapted, so his body continues to rely on carbs rather than ketones. In fact, he’s preventing fat adaptation because exogenous ketones can inhibit lipolysis, the breakdown of fat into fatty acids.
Fat adapting takes time and strategy, not supplementation. That’s why I wrote this article — to cover the basics of fat adaptation, what benefits you can expect, and how to structure your diet and lifestyle to promote fat burning.
What Is Fat Adaptation?
Let’s talk a little physiology now. Fat adaptation is one’s ability to convert fat to energy. When a person is fat adapted, they don’t need a steady stream of carbs (glucose) to power their day. Instead, they can tap into a more abundant energy supply: body fat.
This adaptation was an absolute must back in Paleolithic times. In those primal days, our ancestors didn’t have 24/7 access to food. When calories became scarce, their fat mass kept them alive, often for weeks on end. Imagine a fairly lean, 200-pound hunter-gatherer with 10% body fat. That’s 20 pounds of fat, or over 80,000 calories!
Your ability to utilize fat depends, in large part, on the hormone insulin. When insulin levels are low — like during a fast or while eating a ketogenic diet — body fat is broken apart into fatty acids by a process called lipolysis. Next, those fatty acids are burned by cells in your liver, a process called beta-oxidation. This fat burning produces a compound called acetyl-CoA, the precursor to your primary energy currency: adenosine triphosphate (ATP). Just one issue: Fatty acids cannot cross the blood-brain barrier. That means they cannot serve as brain fuel!
Thankfully, burning fatty acids also generates ketone bodies like beta-hydroxybutyrate (BHB), acetoacetate, and acetone. Unlike fatty acids, these ketone bodies are water soluble. They’re able enter the bloodstream and cross the blood-brain barrier with the help of some little proteins called Monocarboxylate Transporters. (Side note: Low-carb, high-fat diets may increase levels of these transporters in rats!) The big takeaway, however, is that ketones make for great brain fuel. Once they reach their destination, ketones are converted to acetyl-CoA, which then enters the citric acid cycle to form ATP.
Voila! Now you know how cellular energy is made from fat to fuel your body and brain!
Fat Adapted But Not Keto?
Earlier you learned that ketosis isn’t synonymous with fat adaptation. Exogenous ketones, for instance, can put you in a state of ketosis while simultaneously inhibiting lipolysis.
But is the converse true? Can you be fat adapted and not in ketosis? Yes, you can. Being fat adapted simply means you can easily access fat (either dietary fat or body fat) for energy. It doesn’t mean that your body will avoid using glucose when it’s available. Therefore, having carbs now and then — provided it’s not excessive — is no problem for folks who are fat adapted.
Consider a fat-adapted athlete enjoying a dinner of steak and two large sweet potatoes. The carbs will surely kick her out of ketosis, but by morning, she’ll be burning fat again. This is an important point: When you’re fat adapted, you can handle a bit of glucose (say, for a particularly intense workout) and rapidly return to fat burning once blood sugar and insulin levels subside.
Benefits of Fat Adapting
People often attribute the weight loss, stable energy, and performance enhancements of a low-carb diet to ketones. But many of these benefits are downstream of fat adaptation. These benefits include:
- Fat loss. Early weight loss on keto is mostly water weight, because depleting your glycogen stores can flush a lot of water down the drain. Fat loss, however, won’t commence until you’re fat adapted (and in a caloric deficit, of course). This could take days, weeks, or even months depending on your physiology.
- Craving control. Compared to carbohydrates, fat is more satiating. High-fat diets reduce hunger hormones like ghrelin and neuropeptide Y, and also enhance the function of leptin, your satiety hormone. Read this article on carb cravings to learn more.
- You need less food. I see this a lot. After fat adapting, folks naturally adjust to a lower caloric load. Hunger hormones are partly responsible, but so is the increase in efficiency of fat usage. In other words, you fulfill your metabolic needs more quickly.
- Steady energy. Relying on glucose is the default state in modern society, but it’s hardly optimal. As blood sugar swings up and down, your energy swings with it. Dietary fat, on the other hand, has very little blood sugar impact. Fat adapting can help you rely less on glucose and more on fatty acids, a more stable source of energy — like a steady burning wick compared to a raging fire.
- Mental performance. When a fat-adapted brain runs on ketones, it creates less reactive oxygen species (oxidative stress) and more ATP compared to a glucose-reliant brain. It’s like upgrading your car to one that drives faster and produces less exhaust.
- Endurance capacity. Back in 1980, Dr. Steve Phinney found that people on a ketogenic diet lasted longer on a treadmill than high-carb dieters. Why? Because fat-adapted folks took advantage of fat as fuel, allowing their muscles to conserve more glycogen. In other words, your reserve tank stays full for longer during endurance exercise.
Okay, let’s get to the practical stuff now. How do you become fat adapted?
4 Ways To Become Fat Adapted
Becoming fat adapted isn’t super complicated. It mostly involves diet and lifestyle factors that are well within your control. Here are four ways to get started.
#1: Eat a low-carb diet
This much should be obvious by now: If you want to fat adapt, you’ll need to restrict carbs. Restricting carbs keeps blood sugar and insulin levels low, which tells your liver to start burning fat and making ketones.
The ketogenic diet is the most popular low-carb approach, but it’s not the only one. A paleo approach to eating often entails 50 to 100 grams of carbohydrates per day. Active folks, in particular, tend to do very well on this regimen. because your carb tolerance depends, among other things, on your activity level. The more active you are, the more carbs you can eat and stay keto-adapted. Less active, less carbs.
Whatever you do, steer clear of empty calories like added sugar. As you’ve probably noticed, added sugar is just about ubiquitous these days. It’s in beef jerky, sauces, dressings, packaged fruits, fruit juices, you name it. Keep a watchful eye on food labels.
#2: Eat more fat
As you decrease your carbohydrate intake, you’ll need to increase dietary fat.
It makes sense — not just from a calorie-needs standpoint, but also because eating fat helps to train your body to utilize it. Plus, dietary fat has a much smaller impact on insulin levels than carbs. This low-insulin state helps you stay in fat-burning mode rather than fat-storage mode.
There’s also something quite satiating about fat. As fat intake goes up, calorie intake tends to go down. I’ve chatted with Greg Glassman (the founder of Crossfit) about this, and he noticed that folks tend to run on about 20% less calories than he’d expect them to on high-fat diets. Anecdotal, I know, but my former coach and LMNT Co-Founder Luis Villasenor has noticed this phenomenon across thousands of his clients as well. To read Luis’ thoughts on the best macronutrient distribution for a keto diet, check out this article.
In your quest for fat adaptation, it’s best to stick to healthy fats like olive oil, coconut oil, nuts, avocados, butter, and animal fat. Somewhere between 50 and 75% of your daily calories is reasonable. That said, fat should not be your focus — getting adequate protein should. After you dial in protein, lever calories from fat up or down to build, maintain, or lose body mass.
#3: Try fasting
When you stop eating for a reasonable period of time, your body still needs energy. Where do you think that energy comes from?
Well, to begin we have a backup store of carbohydrates! The liver and muscles store glucose as glycogen. But those reserves only add up to about 500 grams of glycogen (2,000 calories), which can be used up rather quickly. What happens when you run out of glycogen?
Do we store protein? Sure we do, in muscle tissue! However, our hairy ancestors wouldn’t have lasted very long if their bodies evolved to break down muscle shortly after we stopped eating. No, muscle is quite useful and we like to hang onto it as best we can. In fact, the ketones produced while fasting serve, in part, to protect your muscle mass.
That leaves body fat! When we practice fasting, our bodies have to rely on body fat. Thus, fasting is a valuable tool in your fat adaptation toolkit. If you’re new to fasting, you might start with a 12 hour fast daily, and work your way up as comfort and schedule permit. To learn more about who can benefit from fasting, who should avoid it, and the most important tips for beginners, check out this article.
#4: Exercise
Exercise alone won’t lead to fat adaptation, but it will contribute to making the process easier. Both strength and endurance exercise have been shown to increase insulin sensitivity. The better your body responds to insulin, the faster you can resume fat burning after eating carbs.
High intensity interval training (HIIT) — even just once per week — seems especially potent in this regard. I get my HIIT through jiu-jitsu, but you might get it through sprinting, soccer, tennis, or some other modality. Pick something you enjoy and it won’t feel like work!
How Long To Fat Adapt?
Fat adaptation is a pretty neat state. As we learned today, utilizing body fat for energy can be incredibly helpful for body recomposition, mental acuity, steady energy, endurance capacity, and more. But as we wrap, you may be wondering: How long will it take to fat adapt?
There isn’t a simple answer. The truth is, your fat-adaptation time depends on your genes, proclivity for fasting, dietary choices, and a host of other factors. An elite athlete may take mere days, while a homebody could take months.
To speed up your fat adaptation, eat less carbs and more fat while prioritizing protein first. Be sure to exercise regularly, and — if it makes sense for you — perhaps give intermittent fasting a go. When you start losing fat mass, craving carbs less often, and feeling more stable energy throughout the day, you’ll know it’s working. And if it’s not working, don’t force it. Listen to your body. Low-carb diets just aren’t for everybody.
