Because the brain depends on a steady glucose supply, your body defends blood sugar within a narrow range – with a fixed sequence of responses. As levels drift down, insulin release eases off first, at roughly 81 mg/dL (4.5 mmol/L). At roughly 68 mg/dL (3.8 mmol/L), glucagon and adrenaline rise, followed by growth hormone and cortisol , .

If glucose keeps falling, warning symptoms follow at roughly 58 mg/dL (3.2 mmol/L). In a controlled study, healthy volunteers reported anxiety, palpitations, sweating, irritability and tremor . Some of the sensations we call anxiety are part of the body's fuel alarm – driven by the same adrenaline that protects the brain.

This does not mean anxiety disorders are “just blood sugar”. In healthy people, the defences usually stop glucose from falling that far. But it explains why long gaps, skipped meals and coffee-only mornings can amplify restlessness, irritability and poor focus. The everyday version even has a name: in a three-week study with 9,142 mood ratings, greater hunger went along with more anger and irritability and less pleasure .

Overnight, your liver keeps the brain supplied from its glycogen store – around 80 g on average . If dinner was early and small, that reserve gets tested. Waking at night with a racing heart, sweating or restlessness can have many causes: sleep apnoea, thyroid problems, menopause, alcohol, stress – and in people with diabetes, low blood sugar. Get it checked. Testing a carb-containing evening meal is a low-risk experiment (see Refuel).

In large cohort studies, whole fruit is linked to a lower risk of type 2 diabetes, while fruit juice is linked to a higher one . The practical point from the seminar still holds: on its own, a piece of fruit is a small snack, not a meal. Combine it with oats, yoghurt or quark for a steadier curve.