You're Eating Less. You're Exercising More. So Why Are You Exhausted?
- Renee Kindler NP
- 4 days ago
- 7 min read
When women are exhausted, struggle with stubborn weight changes, poor recovery, or symptoms that seem to point to hormonal imbalance, the first assumption is often that they're eating too much of the wrong foods.
Or maybe they're simply not exercising enough.
So they do what they've been told to do.
They cut calories. They skip meals.
They cut back more on carbohydrates or fats. They add another workout. They push through the fatigue because surely, if they're a little more disciplined, their body will eventually cooperate, like it used to.
What if you're asking your body to do more while giving it less energy to work with?
This approach may produce short term changes on the scale, but it can create significant stress in the body over time. When the body senses energy intake is consistently lower than its needs, it starts adapting. These adaptations can impact energy levels, metabolism, hormones, recovery, mood, immune function, and even body composition.
Sometimes the more important question is not whether you're doing enough.
It's whether you're giving your body enough to support everything you're asking it to do.
This is where the idea of underfueling becomes interesting.
What Is Underfueling?
Underfueling doesn't necessarily mean starving yourself or surviving on a few hundred calories a day. You can be eating what looks like a perfectly reasonable amount of food and still not be providing enough energy for your individual needs, particularly when exercise, daily activity, stress, and other demands are high. In many cases, people consume enough calories to get through the day, just not enough to support optimal physiological function. This can be common among active individuals, parents, busy professionals, athletes, and chronic dieters.
"Low energy availability" has gained attention in recent years. It refers to a state where the body doesn't have sufficient energy remaining after exercise and daily activities to support essential functions such as hormone production, cellular repair, metabolism, and reproductive health. Research has shown that low energy availability can negatively affect multiple body systems, even over relatively short periods. The concept has been studied most extensively in athletes. This is where the conversation gets more complicated than “calories in, calories out.”
What Happens When Your Not Eating Enough
Your body isn't using food only to fuel your workout.
It needs energy to keep your brain functioning, your heart beating, your immune system working, your muscles repairing themselves, your body temperature regulated, and your tissues maintained.
Think about a woman who has gradually become much more active.
She used to walk occasionally. Now she's walking every day, strength training three times a week, adding cardio, and trying to stay on top of everything else in her life.
Her food intake may not have changed much.
But her demands have.
That matters because energy requirements are individual. There isn't one calorie number that tells us whether a person is adequately fueled.
The same meal plan can be plenty for one person and insufficient for another.
The context matters.
When energy availability stays too low for long enough, the body can adapt.
People describe this as starvation mode, but the physiology is more nuanced.
Your body doesn't simply stop losing weight and begin storing every calorie you eat.
Instead, energy expenditure and other physiological processes can change as the body responds to reduced energy availability. Some of these responses are normal adaptations to a temporary energy deficit. When low energy availability becomes prolonged or severe however, the effects can extend to endocrine and reproductive function, focus and attention, bone health, immune function, exercise performance, and metabolic health.
One of the more fascinating pieces is that you don't necessarily see all of these changes happening.
You may still be completing your workouts. But maybe you're moving less during the rest of the day.
You sit more. You stop taking the stairs.
You don't have the same energy to be as active with your family after work.
You may not consciously decide to do any of those things. Your body simply becomes more economical.
So you're thinking:
I'm exercising more. Why isn't this working?
Meanwhile your body may be thinking:
We're spending more energy than we're getting. Let's conserve where we can.
That's not your metabolism breaking. It's your body adapting to the circumstances you're giving it. This is one reason why continually cutting calories isn't necessarily the logical next step when progress slows. Research has shown that low energy availability can reduce resting metabolic rate and impair the body's ability to maintain normal physiological function. These adaptations are designed to conserve energy during times of perceived scarcity.
Sometimes the question isn't: “How can I create a bigger deficit?” Rather its “What's my body already doing to compensate for the deficit I'm creating?” That is a very different question.
Underfueling, Nutrition, and Your Thyroid
There's another part of this story that deserves far more attention, particularly when we're talking about metabolism and the thyroid.
Your thyroid is a heavy nutrient dependent organ.
We often talk about the thyroid as though it simply controls whether your metabolism is fast or slow. Thyroid physiology is much more complicated than that. Your thyroid needs specific nutritional building blocks to make and metabolize thyroid hormones.
Iodine is required to make thyroid hormones. Selenium is involved in enzymes that help regulate thyroid hormone metabolism. Iron is required for thyroid peroxidase, an enzyme involved in thyroid hormone synthesis.
That doesn't mean eating too little automatically causes thyroid disease.
It certainly doesn't mean everyone with fatigue, weight changes, or feeling cold needs an iodine or selenium supplement. in fact, excess iodine can actually interfere with thyroid function in susceptible people.
The more useful point is this: Your body needs both energy and nutrients. These aren't interchangeable. You can consume enough calories but have a diet lacking nutritional variety. You can eat highly nutritious foods, but not enough total energy. That's why the word healthy can be misleading.
A small smoothie can be healthy.
A salad can be healthy.
A carefully portioned dinner can be healthy.
However, a day made up of small portions of healthy foods may still fail to meet the needs of a woman who is exercising regularly and living a very active life.
The problem isn't that the foods are bad.
The problem is that healthy food and adequate fueling aren't necessarily the same thing.
Inadequate energy intake may lead to metabolic adaptation. This can show up as:
● Weight loss plateaus
● Feeling cold frequently
● Reduced energy expenditure
● Increased fatigue
● Decreased exercise performance
● Difficulty maintaining previous weight loss
How Underfueling Can Impact Hormones
Perimenopause is already a period of significant physiological change. Hormone patterns shift. Sleep can change. Body composition can change. The way your body responds to dietary restriction and exercise may not feel exactly the same as it did in your 20s or 30s.
Research shows meaningful changes in body composition across the menopause transition, including increases in fat mass and changes in lean mass. Those changes aren't caused by hormones alone. Aging, physical activity, diet, sleep, and other factors all contribute. So if it feels like your body starts behaving differently in your 40s, that doesn't automatically mean you've become less disciplined. It doesn't automatically mean your hormones are the entire explanation either.
Thyroid Hormones
The thyroid plays a major role in regulating metabolic rate.
Research has demonstrated low energy intake can reduce the production and activity of thyroid hormones. This may contribute to symptoms of fatigue, cold intolerance, sluggishness, and difficulty losing weight despite continued dieting efforts.
Reproductive Hormones
The reproductive system is particularly sensitive to energy availability.
In women, chronic underfueling may contribute to irregular menstrual cycles, fertility challenges, and reduced estrogen production.
In men, low energy intake can contribute to reductions in testosterone production, which may impact muscle maintenance, recovery, energy levels, and overall well-being.
The body often views reproduction as non-essential during periods of energy scarcity.
Could Underfueling Be Contributing to Your Fatigue and Exhaustion?
Symptoms alone can't tell you whether you're underfueled. Persistent fatigue, unexplained weight changes, or changes in exercise tolerance may also warrant evaluation for things such as thyroid disease, iron deficiency, sleep disorders, medication effects, hormonal changes, or other medical conditions.
Signs You May Not Be Eating Enough
Signs of underfueling are often subtle and may be mistaken for unrelated health concerns.
They may include:
● Persistent fatigue and exhaustion
● Frequent hunger and food cravings
● Trouble focusing
● Poor sleep quality
● Feeling cold frequently
● Hair thinning
● Mood changes or irritability
● Reduced exercise performance
● Slow recovery from workouts
● Menstrual irregularities
● Weight loss resistance despite dieting
Experiencing one or two of these symptoms does not automatically mean you are underfueling. However, a pattern of multiple symptoms may warrant a closer look at overall energy intake and nutritional adequacy.
Maybe Your Symptoms Are Information
I don't want you reading this and deciding “Aha. That's what's wrong.”
I want you to consider something different.
Maybe your symptoms are information.
Maybe your body isn't failing you.
Maybe it's responding to the conditions it's been given.
Food provides energy and nutrients. Exercise creates a demand.
Sleep and recovery allow the body to adapt. Hormones influence these processes.
When one part of that picture changes, the others don't necessarily remain unchanged.
That's why the answer isn't always another diet. It isn't always another workout or another supplement.
Sometimes the better question is: What is my body being asked to do and does it have what it needs to do it?
The goal isn't to win a contest against your body. It is to understand what your body needs in this particular season of your life...and then listen.
It really is talking to you.
References:
Areta, J. L., Taylor, H. L., & Koehler, K. (2021). Low energy availability: History, definition and evidence of its endocrine, metabolic and physiological effects in prospective studies in females and males. European Journal of Applied Physiology, 121(1), 1–21.
Greendale, G. A., et al. (2019). Changes in body composition and weight during the menopause transition. JCI Insight, 4(5), e124865.
Köhrle, J. (2023). Selenium, iodine and iron—Essential trace elements for thyroid hormone synthesis and metabolism. International Journal of Molecular Sciences, 24(4), 3393.
Mountjoy, M., et al. (2023). 2023 International Olympic Committee's (IOC) consensus statement on Relative Energy Deficiency in Sport (REDs). British Journal of Sports Medicine, 57(17), 1073–1097.
Nolte, J., Kirmse, M., de Marées, M., & Platen, P. (2025). Effects of short-term low energy availability on metabolism and performance-related parameters in physically active adults. Nutrients, 17(2), 278.
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* These statements have not been evaluated by the Food and Drug Administration. Any products mentioned in this article are not intended to diagnose, treat, cure, or prevent any disease. The information in this article is not intended to replace any recommendations or relationship with your health care provider.
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Renee Kindler is a Nurse Practitioner who utilizes functional medicine to support you to find the root cause of illness and addresses imbalances that can make you ehausted. If you’re ready to dive deeper into functional medicine for thryoid, sleep, or hormone support, Renee is available for 1:1 consultations.
Find out more at www.reneekindler.com or click button to schedule a call today!
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