there are more than a few people with fatigue and adrenal problems who cured themselves with a high Sugar diet in the form of sweet fruit.
i like the simplicity of it, if your blood Sugar is low then have more sugar.
or even if their blood Sugar isn't low they could still be stressing their body by not providing enough sugar forcing catabolism of muscle tissue to turn into glucose or overdriving the adrenals or pancreas to boost blood sugar.