Power Trim 1200 The majority of the food portions that is recommended when going on a 3 day tuna diet is mostly very unbalanced making it unhealthy for consumption in the long run. The reason is because your weight loss would be just temporary and last a short while. Consider for example, during your 3 day tuna diet your dinner might be, small portions of fish and chicken, a little butter, some fruits and vegetables and for some reason suddenly you consume chocolates at the end of the day which would result is a massively unhealthy choice of daily diet.