If there’s one topic that seems to confuse and frustrate women across the lifespan, it would have to be metabolism.
How can you speed up our metabolism? Why does your friend’s weight never budge, no matter what she eats, while you gain 5 pounds overnight? And how might your metabolism be affecting your overall health and wellness?
The secret to all these questions lies in something called metabolic flexibility.
In this article, we’ll learn all about metabolism and metabolic flexibility, and how you can harness its power to improve your health.
Signs of Metabolic Flexibility
If someone you know can eat whatever they want and never gain a pound, they likely have high metabolic flexibleity. Healthy adolescents often have great metabolic flexibility.
Other signs of metabolic flexibility include:
- Maintaining satiety between meals (i.e., not having to eat or snack every few hours)
- Stable level of energy throughout the day
- Not finding yourself getting “hangry” between meals
- Positive response (weight loss) to a low-calorie diet
As we’ll discover in this article, the benefits of metabolic flexibility are profound.
Signs and Symptoms of Metabolic Inflexibility
Your body also provides several clues that indicate it’s having a tough time maintaining energy. A few of those signs include:
- You have trouble losing weight despite eating less.
- You’re overweight.
- You get irritated or “hangry” if you don’t eat every 2 or 3 hours.
- You constantly lack energy during the day.
- You crave caffeine or sweets to “wake up” and get an energy boost.
- You feel like you’re always hungry.
If these symptoms sound familiar, there’s a good chance you need to improve your metabolic flexibility. Doing so can eliminate these unwanted symptoms, and also improve your health for the long-term. Keep reading to understand why.
The Origins of Metabolic Flexibility
Our ancestors had no choice but to be metabolically flexible. Sometimes they had lots of food, and sometimes they didn’t. But the ability to store fat in their bodies allowed them to survive in times when food was scarce because their metabolism would simply switch fuel sources.
During the fed state, the generous supply of glucose (simple sugar) would encourage the body to burn glucose and suppress fat burning. In the fasting state, the human body’s preferred fuel source is actually fat, which leaves glucose for our brain. The communication and cooperation between the two fuel sources ensured that our ancestors’ energy supply and demand were balanced at the cellular level.3 Our ancestors’ daily living was also characterized by abundant exercise, often during fasting conditions.
Today, we have unprecedented levels of food supply. Many people snack throughout the day in addition to their meals, further increasing their calorie intake. Research shows that the continuous delivery of glucose and fat creates a rigid state in our cells. This effect is only magnified when combined with physical inactivity.4
Some experts fear that this metabolic inflexibility underlies the epidemic of metabolic diseases that burden our healthcare systems.5
To understand the importance of metabolic flexibility, let’s take a step back and discuss metabolism.
What is Metabolism?
Many people think metabolism just refers to how quickly your body burns calories. The faster your metabolism, the lower your body weight. But it’s a little more complicated than that.
Scientifically, metabolism is the “catch-all” word for all the chemical processes in your body’s cells, including the breakdown of food and drinks into sources of energy. It’s also necessary for basic functions like:6
- Regulating body temperature
- Managing hormone levels
- Building and repairing cells
- Circulating blood
Metabolism can be divided into two main categories, catabolism and anabolism, which can be used to describe conditions in your body. Simply put:
- Catabolism is the process of breaking down food and drink into their simpler forms, thereby releasing energy.
- Anabolism is the opposite of catabolism. It requires energy to build and store complex molecules from simpler ones. Products resulting from anabolic reactions include sugars, certain fats, proteins, peptides, bone mineralization, muscle mass, and even DNA.7
For example, glucose synthesis is an anabolic process, while its breakdown is a catabolic process.
Your metabolism works non-stop, even while you’re asleep. We depend on it for our survival. But many factors can affect your metabolic rate, or the rate at which your body uses calories. A few such factors include:
- Physical activity
- Body composition
Your metabolism’s efficiency affects your metabolic flexibility. This means that you have to work at being metabolically fit, just like you exercise to stay physically fit.
The Importance of Metabolic Health
Having good metabolic health goes beyond being at a “normal” weight. In fact, results from the National Health and Nutrition Examination Survey 2009-2016 suggested that just 12% of American adults have optimal metabolic health.8
But what does having good metabolic health really mean?
Unfortunately, there’s no consensus on what defines metabolic health. Some experts say it’s the same as the absence of metabolic syndrome; others say the term isn’t aimed at specific risk factors. Instead, they say it’s a health status — “a high level of health and low risk of impending cardiometabolic disease.”9
The optimal cardiometabolic features are defined as:10
- Waist circumference <102 cm for men, <88 cm for women
- Glucose level <100 mg/dL and HbA1c <5.7%, without diabetes medication
- Systolic blood pressure (the pressure in your arteries when your heart beats) <120 mm Hg; diastolic blood pressure (the pressure in your arteries when your heart rests between beats) <80 mm Hg, without blood pressure medication
- Triglycerides (a type of fat in your blood) <150 mg/dL
- High-density lipoprotein cholesterol (the “good” cholesterol) ≥40 mg/dL for men, ≥50 mg/dL for women, without cholesterol medication
Levels that fall outside of these optimal ranges increase your risk of metabolic syndrome, which could lead to serious conditions like:11
- Coronary heart disease
- Heart failure
- Chronic inflammation
- Polycystic ovary syndrome (PCOS)
- Pregnancy complications
- Sleep apnea
- Certain cancers
- Type 2 diabetes
While being overweight and obese are major risk factors for metabolic syndrome, they’re not the only ones. In the National Health and Nutrition Examination Survey 2009-2016, investigators were surprised to learn that less than one-third of normal weight adults were metabolically healthy.
This means people who are at or below normal weight are at risk of developing diseases traditionally associated with obesity.
The Relationship Between Metabolic Flexibility and Metabolic Health
Metabolic flexibility is key for a healthy metabolism. Let’s start with what happens when a metabolically flexible individual eats a meal:
- Your insulin levels rise in response to rising blood sugar levels, which prompts your cells to absorb and store it.
- Once your blood sugar levels stabilize, your insulin levels decline.
- Insulin levels are reduced (to a point) the longer you go between meals. Intermittent fasting has been shown to be an effective non-medicinal treatment option for individuals with type 2 diabetes, but it should be done under the guidance of a physician.12
- When your insulin is low, your body burns stored fat for energy.
As we’ve discussed above, a metabolically inflexible body is less able to tap into the stored fat for fuel. For this reason, there is an increased reliance on carbs and a decreased reliance on fat for energy.
The Relationship Between Metabolic Flexibility and Mitochondrial Health
Metabolic inflexibility also appears to be linked to impaired mitochondrial function, a relationship that is thought to have developed during the course of evolution.
As we discussed above, human physiology evolved during a time when there were alternating periods of feast and famine. The easy transition between fuel choices that helped our ancestors survive has been replaced by chronic overnutrition – a continuous influx of excess calories – in combination with low energy consumption. At the cellular level, this imbalance puts stress on your mitochondria and may lead to irreversible damage over the long-term.13
A 2007 study of metabolically flexible and inflexible subjects found higher mitochondrial density in the flexible subjects. These subjects were also able to burn fat better on a high-fat diet.14 Results from other studies suggest mitochondria in metabolically inflexible individuals are unable to increase replication of their DNA to meet demands and differ in their appearance.15
In essence, having few mitochondria that don’t function properly severely limits the amount of energy your cells can produce.
Not only does it make switching fuel sources more difficult, your body is also not efficiently burning the calories you’re taking in. Calorie excess further overwhelms your mitochondria and drives insulin resistance.16
Insulin resistance is where the real trouble starts. Because your body is having a harder time burning glucose, it’ll have an even harder time burning body fat.
To make matters worse, your pancreas will over-secrete insulin to compensate for the high glucose levels. Over time, the insulin-producing beta-cells in your pancreas wear out, causing a decrease in insulin levels.
The Benefits of Metabolic Flexibility
The consequences of metabolic inflexibility are apparent. On the other hand, metabolic flexibility has the following far-reaching benefits to your health:
1. Boosts Fat Loss
Tapping into your fat storage for energy means less fat stored in your body. And despite what many of us tend to believe, a high-fat diet doesn’t lead to weight gain.
In fact, studies show the opposite.
In one trial, 53 healthy, obese female volunteers were randomized into one of two groups:
- A very low-carb diet in which they could eat as much as they wanted
- A calorie-restricted, low-fat diet (30% of the calories coming from fat)
Of the 42 women who completed the study, those in the very low-carb diet group lost more weight compared to the low-fat diet group.17
Another trial compared a low-carb diet to a healthy-eating diet (per the Diabetes UK nutritional recommendations) in both diabetic and non-diabetic patients. The investigators found that the patients in the low-carb diet lost more weight than those in the healthy-eating group.18
2. Increases Mental Clarity and Focus
When your body is low on glucose, your liver turns fat into ketones and sends them into your bloodstream. The ketones are then available for your body to use as fuel.
Ketones are an important energy source for your brain because they bypass the blood-brain barrier.19 In clinical studies, ketogenic diets have been shown to have modest benefits in patients with certain cognitive disorders, including Parkinson’s disease and Alzheimer’s disease.20
Some studies also show improved mental clarity and focus for ketogenic dieters. In a small study, 19 women were placed on either a low-carbohydrate diet or a reduced-calorie balanced diet. They were asked to perform a battery of cognitive tasks, including a few that assessed their visuospatial memory, attention, memory span, and mood. The women on the low-carb diet responded faster during the attention task and had better mood than those on the balanced diet.21
Another study assigned 23 adults with mild cognitive impairment to either a high-carb diet or a very low-carb diet for 6 weeks. The investigators observed several improvements in the subjects eating a low-carb diet, including:22
- Weight loss
- Reduced waist circumference
- Lower fasting glucose level
- Lower fasting insulin level
In short, metabolic flexibility appears to have certain cognitive benefits. However, more studies will need to be conducted to confirm these benefits.
3. Improves Insulin Sensitivity
Your body may become more insulin sensitive as a result of fat oxidation. A state of ketogenesis (burning fat) promotes insulin receptor sensitivity and reduces the fluctuation of insulin secretion.23
Studies in human subjects focusing on the role of a low-carb diet on insulin sensitivity are limited. One study compared the effects of a low-carb, high-unsaturated fat, low-saturated fat diet to a high-carb, low-fat diet in obese patients with type 2 diabetes. Both groups achieved substantial weight loss, but the low-carb diet group achieved greater improvements in their lipid profile and blood glucose stability.24
Because obesity is closely related to insulin resistance, it can be expected that weight loss can improve insulin resistance in diabetic patients.
4. May Improve Mitochondrial Function
Impaired mitochondrial function is often associated with a decline in energy production, which can promote or worsen chronic disease.25
And because your skeletal muscle accounts for approximately 90% of insulin-mediated glucose uptake, mitochondrial dysfunction in skeletal muscle is linked to insulin resistance and type 2 diabetes.26,27
A study published in 2020 evaluated 29 physically active adults who completed a 12-week exercise program and either a ketogenic diet or their habitual mixed maintenance diet. The ketogenic diet increased ATP (your primary energy currency) production and mitochondrial respiratory control ratio.28 The respiratory control ratio is a useful measure of mitochondrial function; a higher ratio indicates good function, while a low ratio indicates impairment.
How Do You Improve Your Metabolic Flexibility?
If you’re worried about your metabolism, the good news is that there are things you can do to improve your metabolic flexibility. Here are my recommendations:
1. Focus on Your Diet
Your diet has a direct impact on your metabolic flexibility. Even the best supplements can’t outperform a poor diet.
Many of the studies we discussed above showed the benefits of a low-carb, high-fat (or ketogenic) diet. This gives your body an opportunity to burn fat or ketones. This can be accomplished by lowering your carb intake throughout the day and increasing your overnight fasting window.
It may also help to stay hydrated and test your blood sugar and ketone levels regularly. Keeping a log will give you data on the impact these changes have on your body.
The truth is, going cold turkey into a ketogenic diet can be uncomfortable for many people. A slower approach, with a focus on clean eating, is generally safer and easier to tolerate. In general, I recommend the following foods:
- Fiber-rich green vegetables
- Clean proteins like pasture-raised eggs, poultry, and meats
- Omega-rich foods
- Berries to offset cravings
- Chia seeds
- Monk fruit
A low carb diet with plenty of whole foods and healthy fats can make a huge difference in your metabolic flexibility.
2. Develop Mindful Eating Habits
In our modern lives, there is a growing disconnect between humans and the food we consume. And with so many options at our fingertips, we’ve become accustomed to picking out what is often purely sensational – addictive, processed foods.
We also take little time to appreciate how our bodies respond to the food we consume. To avoid chronic overnutrition, I recommend slowing down. Even before you eat, sit with your hunger and work through it. What type of hunger is it? Are you really hungry? Is your blood sugar low? Or are you needing stimulation? It’s important to get in tune with what your body actually needs at the moment.
3. Reduce Stress and Rest
Stress has a profound effect on your entire body. Chronic stress is associated with an increased risk of metabolic disease, including obesity and type 2 diabetes.29 Research has also shown that sleep deprivation can affect glucose metabolism and hormones involved in regulating your metabolism.30
Getting plenty of rest is essential especially when you’re making dietary and lifestyle changes. Read about my 10 healthy stress hacks in Into the Blue.
4. Choose the Right Supplements
There are several supplements I frequently recommend for my patients seeking greater blood sugar control and metabolic flexibility.
Clean nutritional products like ketogenic shake mix and collagen powder can help provide a smooth transition into a new way of eating. Probiotics and herbal supplements support healthy energy balance and glucose metabolism.
Login to the dispensary here to view a complete list of recommended products for metabolic flexibility.
Take Control of Your Metabolic Health
Achieving metabolic flexibility is essential for optimal health. But with all the fad diets out there, it’s hard to know what’s right for you.
If you’re tired of not being able to lose weight or you’re concerned about your risk for diabetes or heart disease, I’m here to help. As a women’s health expert, I work with women of all ages to develop a personalized plan that will help you achieve metabolic flexibility.