'Unpleasant side effects can occur with the Atkins diet. To start with, burning fat results in the production of substances called ketones as your body enters a state called ketosis. This can result in bad breath, tiredness, weakness, dizziness, insomnia and nausea. Constipation may also occur as a consequence of avoiding typically high-fibre foods such as fruit, veg, beans, wholewheat pasta, brown rice, wholegrain breakfast cereals and jacket potatoes.' - taken from a diet reveiew website.