Another factor in all of this is messed up hormones, specifically the thyroid, which regulates metabolism and energy. Things which destroy the thyroid (and which are very difficult to avoid):
1. Fluoride in water
2. the flour used in most breads is also a thyroid inhibiter.
3. Various other chemicals like MSG, which affects your adrenal glands, and indirectly hurts your thyroid because of the adrenal-thyroid connection.
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Bottomline: When people have a weak thyroid, then their adrenals compensate to try to attain balance. When people's adrenals get overworked, they feel tired, so they resort to caffeine, carbs or both for energy. This whole unbalanced process leads to poor sleep, loss of nutrients and lots of stress.
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Stress leads to further cravings for Vitamin C (most people choose sweets) and Omega 3 oils (most people choose bad, fatty foods). This leads to weight gain and further stress on the thyroid/adrenals. The cycle is hard to break. But nutrition, avoiding thyroid inhibitors, and exercise are the key.
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Thyroid nutrients - Get IODINE through Kelp vitamins, or iodide supplements, detoxified iodine liquid drops (look up Edgar Cayce), or the supplement "Atomidine".
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Adrenal nutrients - Vitamin C. Good, healthy salts ("real salt" company). Good, omega3 oils.