Depending on the severity and duration of  IGT symptoms vary from subtle to more severe, the symptoms below are listed in order of subtlest to more severe cases.

 

Carbohydrate Cravings

 

• Urge for sweet or starchy foods

 

In individuals with impaired glucose tolerance, when glucose levels drop rapidly after a spike, the brain, particularly glucose-sensing neurons in the hypothalamus, detects this decline and activates compensatory pathways to restore energy balance. 

 

This process stimulates the autonomic nervous system and the release of counter-regulatory hormones such as adrenaline and cortisol, which heighten hunger and the drive to seek quick sources of glucose. Research demonstrates that during experimentally induced hypoglycaemia, food cravings increased more than 4 fold, with the strongest urges directed toward high-carbohydrate foods. 

 

This occurs because glucose is the brain’s principal energy substrate, and low circulating glucose levels impair neuronal function, prompting an adaptive response to rapidly replenish it. Consequently, people with IGT experience greater post-meal glucose swings and reactive hypoglycaemia often develop cravings for sweet or starchy foods. [64]

 

Localised Abdominal Weight 

 

Research shows IGT doesn’t just make it harder for the body to use sugar properly, it also changes where fat is stored. Large genetic studies have found that people who are more prone to poor glucose metabolism tend to carry extra weight around the waist and belly, even if their overall body weight isn’t very high. 

 

This happens because when the body stops responding well to insulin, the fat under the skin doesn’t store energy as effectively, so more fat ends up being deposited deeper in the abdomen, around the organs. Studies confirm this link, showing that genes connected to insulin resistance ( poor sugar metabolism ) also encourage central fat gain. [54][55]

 

Energy Depletion Associated with Missed Meals

 

• Faintness

• Dizziness

• Trembling or weakness 

 

In IGT, the body's cells do not respond optimally to insulin, which causes glucose levels to elevate within the blood. In this circumstance, the body attempts to compensate by prolonging the secretion of insulin in order to lower the elevated blood sugar levels. This sustained hyperinsulinaemic response can precipitate a significant decline and exaggerated drop in blood glucose many hours after consuming the meals. This level of decline can manifest as sensations of faintness or dizziness when missing a meal, or on the upper end trembling and weakness [6]. 

 

Xerosis and Ichthyosiform - Dry Skin + Cracked Heels

 

• Very dry or scaly skin on the lower legs, feet and hands

• Cracked Heels 

 

Dry skin (xerosis) and fish-scale-like skin (ichthyosiform changes) are very common in people with poor sugar control, affecting around 40% of patients overall. These changes usually appear on the lower legs and feet, and less often on the hands. 

 

It occurs because diabetes can damage small nerves that control sweating, leading to reduced moisture in the skin. Over time, poor circulation and the buildup of sugar-damaged proteins, known as advanced glycation end-products further weaken the skin’s barrier, slowing natural cell renewal. As a result, the skin becomes dry, rough, and scaly. [61] 

 

Poor blood sugar control also contributes to cracked heels through several structural and biochemical skin changes, which cause collagen fibers in the skin to stiffen and lose elasticity. This, combined with reduced hydration of the stratum corneum results in drier, less flexible skin that is prone to cracking, particularly on pressure-bearing areas such as the heels. This is further demonstrated in research which has highlighted 92 - 100% of diabetic participants exhibited some form of heel skin cracking. [68]

 

Recurring Infections 

 

• Urinary Tract Infections

• Oral Candidiasis

• Vaginal Candidiasis

• Fungal Nail Infection  

 

Poor glucose regulation, as in impaired glucose tolerance or diabetes is strongly associated with recurrent infections, notably yeast and urinary-tract infections. Elevated blood glucose creates multiple converging problems, firstly it feeds yeasts and bacteria directly via increased sugar in saliva, urine and mucosal secretions. It also impairs immune cell function and micro-circulation, and in the urinary tract it promotes microbial growth and retention of infected urine. 

 

In one study comparing 15 studies of 827,948 participants, UTI prevalence was estimated to be 11.5% higher in those with poor sugar metabolism in contrast to healthy controls. [59] 

 

In parallel, those with high blood-sugar levels have a markedly higher incidence of yeast and fungal infections. Studies have demonstrated that in people with diabetes or impaired glucose tolerance, Candida colonisation occurs far more frequently than in the general population, with oral candidiasis affecting approximately 68 - 84 % of diabetic individuals compared with only 27 % of non-diabetics. 

 

Vaginal candidiasis shows a similarly higher burden, with 18.8 % of women with type 2 diabetes infected versus 11.8 % in healthy controls, and recurrence rates markedly higher when HbA₁c levels exceed 8 %. 

 

Furthermore skin and nail infections such as fungal nails are present in up to 84 % of diabetics with peripheral neuropathy or vascular compromise, which is about 2.5 times the rate seen in non-diabetic populations. [60] 

 

Anxiety Symptoms

 

25% increased risk of anxiety symptoms including:

 

• Racing thoughts

• Scattered thoughts

• Hypervigilance

• Overwhelm

• Irritability

• Impatience

• Restlessness

 

Impaired glucose metabolism contributes to heightened anxiety risk through both physiological and neurochemical mechanisms. Fluctuating or chronically elevated blood glucose levels activate the hypothalamic–pituitary–adrenal (HPA) axis, increasing the release of stress hormones such as cortisol and adrenaline, which in turn stimulate sympathetic nervous system activity, reinforcing anxious arousal and anxiety symptoms.

 

Supporting this, a large systematic review of 12 studies and 12,626 individuals with impaired glucose control, found individuals were 25% more likely to experience anxiety symptoms than non-diabetic controls. [65]

 

Depressive Symptoms

 

35% increased risk of depressive symptoms

 

• Sadness

• Pessimism / Negativity

• Loss of pleasure

 

Persistently elevated glucose levels trigger systemic inflammation, increasing proinflammatory cytokines which interfere with serotonin synthesis. This has been clinically demonstrated in a review of 24 independent papers examining the relationship between blood-sugar regulation and depression. The results demonstrated individuals with poor glucose control and subsequent high blood sugar are significantly more likely to experience depression than those with normal glucose levels, with an approximate prevalence of 35%. [66]

 

Neuropathy of the Hands and Feet 

 

• Pins and Needles

• Burning Sensation or Pain

• Numbness - Advanced stages 

 

Long-term high blood sugar damages the small blood vessels that supply nerves, especially in the feet and hands. Over time, this causes a loss of nerve function, particularly in the sensory nerves. This can manifest as first feel burning, tingling like pins and needles, or pain in the hands and feet particularly at night or on during rest, and in more advanced stages numbness or loss of sensation can occur. It is estimated that 40% of neuropathy cases are associated with having IGT [7][8][53] 

 

Skin Tags

 

Skin tags are small, benign skin growths often found on the neck, under the breasts, armpits, eye lid area, or thighs and groin, and can serve as a visible clue to IGT. Research shows that elevated insulin levels as the result of poor sugar metabolism can stimulate growth factor-receptors such as the insulin-like growth factor-1 receptor (IGF-1R) in skin fibroblasts and keratinocytes, which promotes local proliferation of skin cells and the formation of tags. [56]

 

Moreover, the presence of multiple skin tags strongly correlates with the measures of poor sugar control. In one study, individuals with multiple tags had substantially higher odds of insulin resistance / IGT, compared to those without, often in the 40 - 70% higher probability range. [57]

 

Cognitive impairments

 

• Memory Decline 

• Poor word recall 

 

Cognitive impairments can be described as a decline in cognitive abilities such as concentration, memory, and verbal fluency. While the brain was traditionally thought to be insulin-insensitive, recent research indicates that poor insulin sensitivity associated with Impaired Glucose Tolerance  plays a role in cognitive health [10].

 

One study following participants with Impaired Glucose Tolerance for 2 - 4 years showed a significant association with memory decline [11]. Another study which administered insulin intranasally for 8 weeks demonstrated a significantly higher word recall in participants, and even reflected enhanced mood and confidence [12]. 

 

Impaired glucose metabolism to varying degrees is associated with decrements in cognitive function and changes in brain structure, with the extent of type 2 diabetes being associated with a 50% increased risk of developing dementia [13].

 

Eye Discomfort + Visual Disturbances

 

• Eye Strain or Pressure

• Blurred close-up focus after sugar rich foods

 

Poor sugar metabolism and excess glucose in the bloodstream draws fluid into and out of the eye’s lens and retinal tissues, temporarily changing its shape and thickness. This process alters how light is focused, leading to blurry or shifting vision that can come and go as glucose levels significantly increase and decrease. 

 

Over time, chronically elevated glucose can damage the tiny blood vessels that supply the retina, leading to reduced oxygen delivery and retinal thinning, especially in the outer nuclear and photoreceptor layers. Studies using retinal imaging show that even people with prediabetes can develop subtle retinal structural changes and visual disturbances before diabetes is diagnosed. 

 

These early visual altercations can manifest as sensations of eye strain or eye pressure. It can also manifest itself as a fluctuating of focus, with temporary blurred vision, particularly close up objects and after consuming high sugar meals. [14][15]

 

High Blood Pressure

 

Insulin resistance, a core feature of impaired glucose tolerance, contributes to increased blood pressure through multiple interlinked mechanisms. Chronically elevated insulin levels stimulate the sympathetic nervous system (SNS) and the renin-angiotensin-aldosterone system (RAAS), promoting sodium and water retention, increasing plasma volume, whilst also inducing vasoconstriction, all of which increase blood pressure.

 

Clinically, this pathway has been demonstrated in large studies, as an example a study of 8,513 adults with hypertension demonstrated that those who tested positive in the highest quartile for insulin resistance had a 49% higher odds of uncontrolled hypertension compared to the lowest quartile of insulin resistant / IGT participants. [67]

 

Polycystic ovarian syndrome - PCOS

 

IGT can lead to excessive production of the hormone insulin, known as hyperinsulinemia. Hyperinsulinemia can play a pivotal role in the aetiology of PCOS as increasing insulin drives excessive ovarian testosterone production and lowers the circulating amount of sex hormone-binding globulin (SHBG) and promotes free testosterone, which constrains follicle formation resulting in irregular menstrual cycles [16].

 

It is important to note that while obesity plays an important role in these metabolic features, defective insulin sensitivity and secretion is also present in lean PCOS patients [17].