The headache that turns out to be dehydration — the long version posts 61–74

Lab testing: if symptoms are severe or persistent, checking electrolytes and minerals (sodium, potassium, magnesium, calcium) and interpreting them in context of losses during weight loss is reasonable.

This follows post #60 rather than contradicting it.

Constipation and hydration: dehydration makes constipation worse. Increasing fluid intake is the first intervention for constipation alongside other measures.

Practical note that does not fit anywhere else. Whatever you conclude from this topic, write down what you did and when. The single most useful thing in your own records is not any individual result; it is that they are dated and consecutive.

For anyone arriving from a search: the marked solution above is the direct answer, and the replies underneath it add the caveats that make it safe to use.

On post #62 — agreed on the reasoning, with one qualification.

The very ordinary causes of week-two malaise: inadequate hydration, low sodium intake, too-rapid calorie deficit, and inadequate sleep are more common causes of fatigue and malaise than compound toxicity.

Lab testing: if symptoms are severe or persistent, checking electrolytes and minerals (sodium, potassium, magnesium, calcium) and interpreting them in context of losses during weight loss is reasonable.

Water intoxication: drinking excessive water (more than a few liters per day for extended time) without electrolyte replacement can cause hyponatremia. This is rare but serious. Balance fluid with electrolytes.

post #68 is right about the mechanism and I think understates the practical bit.

Exercise and electrolyte losses: sweating during exercise increases sodium and potassium losses. Electrolyte replacement during or after intense exercise helps maintain balance.

Coming back to post #69, because the follow-up matters more than the original answer.

Fluid intake: baseline needs increase with gastrointestinal effects and exercise. Thirst is not a reliable guide during appetite suppression. Drinking regularly (not just when thirsty) is prudent.

Picking up post #69: that is the part I would want checked first.

Sodium: losing weight involves losing some sodium. Electrolyte drinks or salty foods help maintain sodium balance. Very low sodium intake on these compounds raises orthostatic symptoms risk.

Potassium: similar to sodium; losing weight involves some potassium loss. Bananas, sweet potatoes, and other potassium-rich foods help. Severe depletion is rare but symptomatic (weakness, palpitations).

Magnesium: deficiency during weight loss is common and symptoms (fatigue, muscle cramps) are nonspecific. Supplementation is inexpensive and low-risk if needed.