When you reduce your carbohydrate intake to a level that doesn't meet your body's needs, the levels of several hormones change in an attempt to keep you energized. Some of these changes may be beneficial in the short term, but over time, they can negatively affect your energy, mood, appetite, and blood sugar levels.
Carbohydrates signal a sense of security and provide energy (Pixbay)
1. Low Carb Intake May Raise Cortisol Levels
Carbohydrates signal a sense of security (feeling full and satisfied after eating) and provide energy. When your intake is reduced, your body often increases cortisol production to release stored glucose. This is part of the body's natural stress response, but chronically elevated cortisol levels can make you feel more stressed, tired, or hungrier than usual.
If your carbohydrate intake is consistently low, your body may respond by producing more cortisol to help regulate your blood sugar and meet your energy needs.
These changes can affect how you feel every day, so it's helpful to understand the signs:
Increased stress levels, even without emotional triggers.
Feeling extremely tired in the middle of the day or experiencing fatigue with increased energy at night.
Increased cravings for food, especially sugars or quick energy sources.
2. Slowed Thyroid Hormone
Healthy glucose metabolism and a balanced carbohydrate intake are crucial for converting T4 hormone into its active form, T3 (thyroid hormones that regulate the body's metabolism, energy use, growth, and development). When carbohydrate intake is too low, this conversion may slow down, potentially affecting metabolism, body temperature regulation, and overall energy levels.
Research has shown that a low-carbohydrate diet may lower T3 levels regardless of calorie intake.
For many, this manifests as subtle but noticeable changes:
Feeling colder than usual
Fatigue
Weight plateaus despite consistent effort
3. New Patterns of Insulin and Glucagon Levels
When carbohydrate intake is drastically reduced, the glucose-regulating hormones insulin and glucagon fluctuate rapidly to maintain stable blood sugar levels, potentially leading to less stable energy levels. Insulin naturally decreases on low-carbohydrate diets because the body has less glucose to process.
At the same time, glucagon levels rise to help maintain blood sugar by releasing stored glycogen and producing new glucose in the liver.
You might notice this through symptoms such as:
Low energy, especially during exercise
Feeling shaky, dizzy, or nervous between meals
Increased hunger when meals are delayed
4. Improved Leptin Sensitivity
When carbohydrate intake is reduced, leptin (the satiety hormone) levels often decrease, but this doesn't always result in increased hunger. As the body adapts to consuming fewer carbohydrates regularly over time, the hormones responsible for appetite and satiety change.
Many people who follow low-carb or keto diets long-term notice an improvement in leptin sensitivity, meaning the brain becomes better able to recognize fullness even when leptin levels in the blood are low.
At the same time, ghrelin (the hunger hormone) often stabilizes or decreases, while levels of other satiety hormones, such as cholecystokinin (CCK), may increase. This change makes it easier to feel full after several meals.
These appetite-related changes may manifest in several ways:
Feeling full faster during meals
Reduced cravings between meals
More stable and regular appetite
5. Reproductive Hormonal Disruption
For some women, consistently low carbohydrate intake may indicate that their total calorie intake is insufficient for optimal reproductive function.
This can lead to a decrease in the brain's production of gonadotropin-releasing hormone (GnRH), which in turn reduces luteinizing hormone (LH) and follicle-stimulating hormone (FSH), the two hormones necessary for ovulation (the release of a mature egg from the ovary) and regular menstrual cycles.
This pattern is common in cases of energy deficiency. It is associated with functional amenorrhea, which results from a dysfunction in the hypothalamus (when the brain's control center stops sending signals that trigger menstruation due to stress, leading to the cessation of menstruation).
Low levels of the hormone leptin can also contribute to this. Leptin helps the brain determine whether the body has enough stored energy for reproduction, and research indicates that a certain level of leptin is necessary to maintain regular menstrual cycles.
When leptin levels drop due to low carbohydrate intake or insufficient energy consumption, menstrual cycles may become irregular even when total calorie intake appears adequate.
Signs of this include:
Irregular or absent menstrual cycles
Increased symptoms of premenstrual syndrome (PMS)
Decreased energy during the second half (lunar phase) of the menstrual cycle
6. Decreased serotonin levels, affecting mood
Carbohydrates play a direct role in helping tryptophan (an amino acid) enter the brain, where it is converted into serotonin (a neurotransmitter that helps regulate many brain and body functions).
Research indicates that carbohydrate intake affects serotonin pathways and satiety signals. Reducing carbohydrates may decrease serotonin production, which can affect mood, appetite, sleep, and emotional regulation.
Many people notice this effect in their daily lives.