How to Achieve Metabolic Flexibility
Written by: the Editors of goop
Published on: January 21, 2021
Updated on: November 14, 2022
Reviewed by: Will Cole, IFMCP, DNM, DC
Intuitive eating—being mindful about what you put in your mouth and when—is an incredible tool. It has the power to change our relationship to food, to draw us into the present moment, to help us tune in to joy and satisfaction on our plates.
That kind of awareness is essential, yet it sometimes falls short of addressing the physical cues that result from our eating habits. Irritability and fatigue are (unpleasant) somatic experiences; anyone who has ever been hangry is familiar with its intensity. Mindfulness can help. But what if there were a complementary strategy that prevented the hangry monster from darkening your doorstep in the first place?
The key, says functional medicine practitioner Will Cole, is to achieve metabolic flexibility. Metabolic flexibility is the body’s ability to adapt and use whatever fuel is available to it (sugar or fat). When we lack it (metabolic inflexibility), we’re more likely to experience fatigue, insatiable cravings, irritability, and more not-so-fun states of being. The single greatest tool for achieving metabolic flexibility, Cole says, is to fast intermittently.
And that’s why Cole’s forthcoming book is so compelling: It harnesses the practice of intuitive eating and the practice of intermittent fasting. In Intuitive Fasting, he presents a new approach to understanding your body’s cues and eating for both satisfaction and restoration. He outlines the most effective ways to fast and helps us understand which foods to eat when to amplify the benefits. (The book includes meal plans, recipes, daily eating schedules—and plenty of flexibility.) Here, he gives us the Cliff’s Notes on how metabolic flexibility works, the impact of leptin resistance, and where to begin if you want to try intuitive fasting.
PS: If you preorder a copy of the book now, you can sign up to get support from Cole, a digital shopping guide, and more exclusive content as part of a four-week intuitive fasting program.
A Q&A with Will Cole, IFMCP, DNM, DC
Metabolic flexibility is the body’s ability to adapt and use whatever fuel is available to it. If you’ve eaten recently, that fuel is glucose, the sugar that’s in your blood. If it’s been a while since your last meal or if all your blood glucose has been used up, that fuel is stored fat. Sugar is the ultimate quick hit of energy, but fat is a much more efficient fuel source for your metabolism.
Think of it like this: Your body is a fire in the fireplace, and the kindling is sugar. This type of fuel provides short, effective bursts of flame to get the fire going, but kindling is quick to burn, it doesn’t last long, and you have to replenish it constantly to keep the fire burning. The same is true of sugar: You get a temporary energy high, then you crash not long after. If you’ve ever eaten a bunch of sweets and then crashed hard, feeling like you needed a nap a few hours later, you’ve experienced this phenomenon firsthand.
In contrast, fat is like a log of firewood. You can put a log in the fire and know that for hours you’ll have a slow and steady fire burning. Fat is the same: It provides sustainable, stable long-term energy for your body.
Having the ability optimally to burn both kindling (sugar) and firewood (fat) to keep your fire going is the definition of metabolic flexibility. People I’ve worked with appear to be stuck in varying forms of sugar-burning-only mode: hangry, fatigued, insatiable cravings, brain-fogged, and irritable. This is metabolic inflexibility or metabolic rigidity. I want people to have food peace and peace with their body—and a lack of metabolic flexibility is the antithesis of that.
“Intuitive fasting” is my term for flexible and intuitive intermittent fasting. You might think those two concepts are paradoxical: How can not eating for an extended period of time be intuitive?
I see on social media people referring to intuitive eating. It sounds nice, but what the heck does it mean, exactly? When your body is out of balance, it can be very difficult to discern what your body really needs to build vibrant wellness. It’s hard to eat intuitively when you’re in a state of imbalance. There’s little clarity there. Is it intuition or an insatiable craving? Is it intuition or a hormone imbalance? Emotional eating is not intuitive eating. Stress eating is not intuitive eating.
For intuitive eating to be more than a fluffy (yet appealing) sound bite, we need some metabolic flexibility. What I call metabolic inflexibility, bound by hangry cravings, is the death of authentic intuitive eating.
In my experience, to grow in intuition and truly hear the still, small voice of what your body loves, you have to gain some metabolic flexibility. Intermittent fasting is a great tool I’ve used to gain metabolic flexibility: The flexible intuitive fasting plan I designed introduces you to new fasting and eating windows each week. It’s like a yoga class for your metabolism—we are expanding and contracting fasting and eating windows to gain metabolic flexibility over time. Cycling through these fasts can help you get in touch with your body and grow your intuition.
Intuitive fasting is different from other types of fasting in that it’s not designed to be difficult or restrictive; it’s not about starvation. It’s about connecting to your body.
Regular insatiable cravings are a sign that you are stuck in sugar-burning mode and would benefit from more metabolic flexibility.
Leptin is a hormone produced in our fat cells, which are not just inactive tissue but an active part of our hormonal systems. One of leptin’s main jobs is to tell our brains to use our bodies’ fat stores for energy, which is key to metabolic flexibility. Leptin resistance occurs when the hypothalamic cells in the brain stop recognizing leptin’s signals. As a result, the brain doesn’t perceive that enough food has come in, and it reads that as starvation.
If leptin resistance happens to you, your brain will turn on all the signals it can to make up for the falsely perceived food deficit. Everything you eat will go straight into fat storage without being used for energy, making the problem worse. Your brain is saving up for the coming famine, even though there isn’t any famine. This can turn your metabolism upside down and make it almost impossible to quell cravings and eat intuitively.
This hormone-resistance pattern is one of the most common hidden drivers of weight gain that I find in patients. When you’re leptin-resistant, you could live in the gym and eat like a rabbit and still have trouble losing weight. Correcting a leptin issue is vital to establishing metabolic flexibility and using fat for fuel. Intermittent fasting is a great way to support healthy leptin levels and, in turn, a healthy weight for your body.
First, find out where you are on the metabolic flexibility spectrum. I adapted the metabolic flexibility quiz in the book and put it online for people to take for free.
After this, it starts with harnessing the best of both food and fasting. A clean, mostly plant-based ketogenic diet—the ketotarian diet—and flexible intermittent fasting work synergistically and amplify each other. A clean keto diet and intermittent fasting both support your body to naturally produce ketones, specifically beta hydroxybutyrate or BHB. This ketone isn’t just a way to burn fat, although that is one benefit. It also is an epigenetic modulator, meaning it acts like a signaling molecule, aiding our body in:
increasing autophagy (cellular recycling)
increasing stem cells
increasing antioxidant pathways
balancing the gut microbiome
increasing BDNF (the brain’s ability to make new neurons)
making healthier mitochondria (cellular energy centers)
These are very important for feeling vibrant wellness. That’s why in Intuitive Fasting, I paired the four-week flexible fasting plan with a cyclical ketotarian food plan. Focusing on foods like:
Avocados and avocado oil
Olives and extra virgin olive oil
Coconut cream, milk, and oil
Sea vegetables (nori sheets, dulse flakes)
Dark leafy vegetables (spinach, kale)
Sulfur-rich vegetables, like Brussels sprouts, cabbage, and asparagus
Nuts and seeds, like macadamias, almonds, and walnuts
Low-fructose fruits like berries
Ketotarian also has vegetarian keto recipe options, so you can add in pasture-raised organic eggs or grass-fed ghee (clarified butter), as well as pescatarian keto options. This is where you bring in wild-caught fish, like Alaskan salmon, with their beneficial omega-3 fats.
While the above foods are the foundation, a cyclical ketotarian approach means we periodically increase clean carbs like fruits, rice, and sweet potatoes a few times a week or a month. Many women especially do well with this cyclical approach, increasing these carbs around their periods, ovulation, or intuitively throughout the week. There is a grace and lightness to this approach.
By pairing this food plan with expanding and contracting fasting windows, we build metabolic flexibility sustainably.
Will Cole, IFMCP, DNM, DC, is a leading functional medicine expert who consults people around the world via webcam and locally in Pittsburgh. He specializes in clinically investigating underlying factors of chronic disease and customizing a functional medicine approach for thyroid issues, autoimmune conditions, hormonal imbalances, digestive disorders, and brain problems. Cole is also the bestselling author of Intuitive Fasting, Ketotarian, and The Inflammation Spectrum.
This article is for informational purposes only. It is not, nor is it intended to be, a substitute for professional medical advice, diagnosis, or treatment and should never be relied upon for specific medical advice. To the extent that this article features the advice of physicians or medical practitioners, the views expressed are the views of the cited expert and do not necessarily represent the views of goop.
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