Over the past decade, low-carb diets and intermittent fasting have become hugely popular – hailed as miracle fixes for weight loss, blood sugar control, and even anti-ageing. But as with many dietary trends, the long-term consequences are often overlooked. At Dr Ryu Natural Medicine, we regularly see clients experiencing the unintended backfire of long-term carbohydrate restriction, especially when paired with extended fasting and excessive protein intake.
In this blog, we’ll explore what recent research and clinical observations are showing:
- What happens when insulin levels are kept chronically low?
- What happens to thyroid function, metabolic health, cortisol, and overall energy balance when carbs are too restricted?
Let’s break it down.
1. The Role of Carbohydrates in Human Physiology
Carbohydrates are not just “fuel” – they’re a critical metabolic signal. Glucose powers the brain, supports ovulation, sustains thyroid output, and suppresses stress hormone production. In natural medicine, we often describe carbohydrates as a “sparker” of energy metabolism.
When glucose is lacking, your body must work harder to maintain blood sugar levels – and this compensation can come at a significant cost.
2. Extremely Low Insulin: Not Always a Good Thing
While chronically high insulin is problematic, extremely low insulin can be just as harmful. Insulin is not only a blood sugar regulator; it’s an anabolic hormone. It helps:
- Drive nutrients into cells
- Prevent unnecessary muscle breakdown
- Support ovarian function and reproductive hormone production
When insulin remains extremely low, we see:
- Poor muscle protein synthesis
- Infertility due to disrupted ovarian signalling
- Sluggish recovery after exercise
- Increased cortisol to compensate for missing fuel
3. Thyroid Suppression and Metabolic Slowdown
Studies and clinical reports have shown that low-carb diets suppress active thyroid hormone (T3). This happens because the body interprets low glucose availability as starvation. As a result:
- T3 drops
- Reverse T3 increases (a stress-induced, inactive hormone)
- Basal metabolic rate decreases
- People experience fatigue, cold hands and feet, thinning hair, and stubborn weight
One study published in Metabolism: Clinical and Experimental (2015) showed significantly reduced T3 levels after just 3 weeks of a ketogenic diet – even in young, healthy individuals.
4. High Cortisol and the Fight-or-Flight State
When carbohydrate is restricted, the body often compensates by raising cortisol to release stored glycogen and break down muscle tissue to convert amino acids into glucose (gluconeogenesis).
This fight-or-flight response, when sustained:
- Increases abdominal fat
- Disrupts sleep
- Weakens immunity
- Contributes to feelings of anxiety, panic, or “wired but tired”
5. Protein Catabolism: Burning Muscle for Sugar
Without enough carbs, the body often turns to protein for sugar production. This leads to:
- Muscle breakdown
- Increased ammonia and nitrogen waste
- Additional stress on liver and kidneys
- Loss of muscle mass over time, especially in women and older adults
Ironically, long-term low-carb diets can lead to sarcopenia (muscle wasting), even in people who are exercising regularly.
6. The Myth of Reversing Diabetes with Keto
While ketogenic diets may temporarily improve blood glucose levels and reduce the need for medication in type 2 diabetics, this is often due to reduced carbohydrate intake rather than improved glucose metabolism.
Emerging evidence shows:
- Glucose tolerance worsens in many people once carbs are reintroduced
- Insulin sensitivity can decline due to prolonged underuse
- Long-term studies show no clear improvement in mortality or cardiovascular outcomes
A 2021 review in Frontiers in Nutrition concluded that the benefits of low-carb diets are largely short-term and not superior for long-term diabetes management compared to balanced dietary approaches.
7. Hypoglycemia, Dizziness, and Energy Crashes
Carb-restricted individuals frequently report:
- Dizziness
- Mood swings
- Energy crashes mid-morning or late afternoon
- Difficulty concentrating
Why? Because the brain and red blood cells rely exclusively on glucose. Without steady carbohydrate intake, blood sugar levels can dip too low, leading to:
- Light-headedness
- Sugar cravings
- Emotional volatility
- Difficulty maintaining exercise intensity
8. Carbohydrate Intolerance vs. Carbohydrate Deficiency
Some individuals are labelled as “carbohydrate intolerant” when they show post-meal glucose spikes or fatigue. But this is often a sign of underlying metabolic dysfunction, not a reason to eliminate carbs entirely.
Improving glucose disposal through:
- Restoring mitochondrial function
- Supporting liver and thyroid health
- Refeeding carbs strategically
…can help individuals become more tolerant to carbohydrates, not less.
9. Women, Hormones, and Fertility: A Special Warning
Women are especially vulnerable to the side effects of low-carb dieting and intermittent fasting. Chronic carb restriction can:
- Suppress ovulation
- Disrupt menstrual cycles
- Cause estrogen dominance or progesterone deficiency
- Delay or prevent conception
At our clinic, we frequently see women diagnosed with “unexplained infertility” who are simply under-eating carbohydrates and over-stressing their metabolism.
Summary: The Metabolic Cost of Chronic Carb Restriction
| Effect | Consequence |
|---|---|
| Low Insulin | Muscle loss, infertility, low recovery |
| Low Thyroid | Fatigue, cold intolerance, low metabolism |
| High Cortisol | Sleep issues, belly fat, anxiety |
| Protein Breakdown | Muscle wasting, nitrogen load |
| Hypoglycemia | Brain fog, cravings, dizziness |
| Carbohydrate Intolerance | Worsened by restriction, not solved |
Dr Ryu’s Take
In natural medicine, we recognize the body’s energy needs as foundational. Carbohydrates – when sourced wisely – are essential for supporting your thyroid, brain, hormones, and reproductive system. Chronically low-carb diets and aggressive fasting regimens may produce short-term results, but they come with long-term costs.
The goal isn’t to “eliminate carbs” – it’s to restore your metabolic flexibility so you can efficiently use glucose and fat, without over-relying on stress hormones to do the job.
Need help rebuilding your metabolism after low-carb burnout?
Visit our clinic in South West London or book a consultation online. At Dr Ryu Natural Medicine, we support your fertility, hormone health, and energy from the ground up – with science, not fads.
