A Functional and Nutritional Medicine Approach to Fatigue
You know that feeling—dragging yourself out of bed after a full night’s sleep, nursing your second (or third) cup of coffee before noon, or skipping workouts you used to enjoy because your body just can’t keep up.
Fatigue is one of the most common complaints I hear in practice. It’s also one of the most misunderstood.
We often label it as “just stress,” “getting older,” or “being busy.” But persistent fatigue isn’t normal — it’s your body trying to tell you something.
Common Biological Drivers of Fatigue
Fatigue rarely has a single cause. It develops when key systems in the body stop working together the way they should—your metabolism, hormones, immune system, and sleep-wake rhythm all depend on one another. When one of these systems drifts off course, the rest have to compensate.
Below are some of the most common ways that breakdown shows up in the body. Each one can contribute to fatigue, but you’ll usually see other signs alongside it.
Blood Sugar Dysregulation
If your energy swings from high to low throughout the day—or you crash hard in the afternoon—your blood sugar may be fluctuating more than it should. Each time your glucose spikes and drops, your body releases cortisol and adrenaline to keep your body and brain fueled. Over time, this constant “energy juggling act” wears out your system, leaving you foggy, irritable, or craving sugar or caffeine just to stay level.
Other common symptoms of blood sugar dysregulation: mid-morning or mid-afternoon crashes, irritability or anxiety when hungry, trouble focusing after meals
Anemia and Oxygen Delivery
You can’t make energy without oxygen. If iron, B12, or folate are low—or if inflammation blocks your body’s ability to use them—your cells don’t get the oxygen they need to power basic functions. Even mild anemia can make everyday activity feel like a workout, and recovery can take longer than it should.
Other common symptoms of anemia and poor oxygen delivery: dizziness or lightheadedness, pale skin or nail beds, frequent headaches
Nutrient Deficiencies
Micronutrients—vitamins, minerals, amino acids, fatty acids—are the tools your body uses to keep everything running smoothly. Your hormones, brain chemistry, immune system, and metabolism all depend on them. When even a few of these nutrients run low, those systems start to slow down and malfunction. You might feel it as low energy, but it can also show up in many other ways: mood changes, muscle tension, restless sleep, or getting sick more easily.
Sometimes this happens because of increased stress or demand. Other times, it’s because your body isn’t absorbing or using nutrients efficiently. Whatever the reason, when your body is missing key ingredients, it can’t perform at its best—and fatigue is often one of the first signs.
Other common symptoms of nutrient deficiencies: low mood or irritability, muscle cramps or weakness, brain fog, poor sleep quality, frequent colds, or slow recovery after exercise
Note: Exactly how deficiency shows up can vary widely—from person to person, and nutrient to nutrient.
Thyroid Dysfunction
Your thyroid acts like your body’s internal thermostat—it controls how fast or slow your metabolism runs. When thyroid hormones dip, every process in the body slows down: how quickly you burn fuel, how fast your brain processes information, and how effectively you regulate temperature. You may notice that you can’t tolerate cold the way you used to, or that your digestion and focus both feel sluggish.
Other common symptoms of thyroid dysfunction: feeling cold when others are comfortable, constipation, unexplained weight gain, thinning hair or eyebrows, and dry skin
Chronic Inflammation
Inflammation isn’t always bad—it’s part of how your body fights infections and heals. But when it stays “switched on” for too long, it starts to steal energy from normal physical and mental functions. Chronic inflammation can stem from many sources—gut imbalances, autoimmunity, lingering infections, or environmental exposures—and often leads to that heavy, unrefreshing fatigue that sleep doesn’t fix.
Other common symptoms of chronic inflammation: joint or muscle stiffness, brain fog, depression or apathy, unexplained aches or pains
Note: The exact way inflammation shows up can vary a lot. For some, it’s mostly physical pain or swelling; for others, it’s mood changes or mental fog. It depends on which tissues or systems are under the most stress.
Sleep Apnea
Even if you spend enough time in bed, poor-quality sleep keeps your body from repairing and resetting overnight. When your breathing stops and starts all night long, your body is prevented from getting into the deep, restorative stages of sleep needed for true energy recovery.
Other common symptoms of sleep apnea: snoring, waking unrefreshed despite enough hours, dry mouth or sore throat in the morning
Why a Functional, Root-cause Approach Matters
Most people who come to me have already seen their doctor and been told their labs look “normal.” Yet they still feel exhausted. That’s because standard bloodwork is designed to detect disease, not early dysfunction.
You can feel awful long before you cross a diagnostic line. Functional testing looks at how systems are operating, not just whether they’ve completely failed. It asks questions like:
How stable is your blood sugar across the day?
Do you have enough nutrients to make hormones and neurotransmitters?
Is your immune system calm or chronically activated?
How well are your cells turning food and oxygen into energy?
Is your digestive system properly digesting and absorbing the food you eat?
These answers reveal where function is breaking down—and where it can be restored.
Once we understand what’s happening in your body, and where support is needed, we can use nutritional medicine (food, targeted supplementation) and practical lifestyle adjustments (sleep, stress, movement) to rebuild function. As physical function improves, your energy naturally follows.
Summary
Fatigue isn’t a diagnosis—it’s data. When we address the underlying chemistry—blood sugar, inflammation, thyroid, nutrient status—alongside lifestyle and environmental factors, energy stops being something you chase and becomes something your body naturally sustains.
That’s the essence of nutritional medicine: restoring function across the systems that regulate how you feel and function every day.