1. The effects of dietary carbohydrate (CHO) content and of tri-iodothyronine (T3) administration on calcium, zinc and phosphate balances and on urinary hydroxyproline output were examined in eight obese subjects undergoing therapy with low energy (2741–3301 kJ/day), high calcium (28.9–35.1 mmol/day) diets.
2. Calcium balances were generally positive at the high levels of intake used, but significantly more calcium was retained when dietary CHO intake (as proportion of total energy intake) was increased.
3. Zinc balances were more positive when the proportion of dietary CHO was high and correlated both with nitrogen balance and with daytime insulin concentration.
4. Urinary hydroxyproline output generally increased with dieting irrespective of dietary CHO content.
5. Administration of T3 (30–80 μg/day) markedly increased zinc loss without affecting calcium balance.