Night work can change the body's response to food, including glucose regulation. But an energy crash does not identify a glucose problem by itself. Fatigue and sleepiness have several possible causes, and the symptom needs to be distinguished from a measured blood-sugar change.[1][2]

What have controlled studies found?

A randomized crossover study in 12 healthy nurses compared mixed-meal responses during simulated day and night shifts. Glucose rose more after the meal during the night condition, and the researchers observed differences in insulin secretion.[1]

Another controlled study in chronic shift workers separated the effects of internal circadian timing from the imposed sleep-and-meal schedule. Circadian misalignment independently reduced glucose tolerance.[3]

These studies measured responses to meals under controlled conditions; they did not diagnose the cause of individual fatigue episodes.[1][3]

Which tests answer the clinical question?

Prediabetes and diabetes are commonly assessed with HbA1c, fasting plasma glucose or an oral glucose-tolerance test. Tests of insulin resistance itself are used mainly in research, according to NIDDK.[4]

The appropriate test depends on the question, risk factors and clinical circumstances.[4]

What is useful to record?

Describe when the symptom occurs relative to sleep, meals, caffeine and work. Note whether it is a need to sleep, a lack of physical energy or another sensation. MedlinePlus distinguishes drowsiness from fatigue, which can help make the description more precise.[2]

Include any existing glucose results and the conditions under which they were collected. A fasting result and one obtained after eating do not represent the same measurement.[4]