I'm not an expert on nutrition either, but do take an interest in these sorts of things. From what I've read, eating one meal a day, provided it is nutritional and contains the appropriate level of fat/protein/calories etc your body needs (taking into account your lifestyle e.g. active/sedentary) won't do you any real harm. However, your energy and concentration levels are unlikely to be at their peak if you are not eating frequently throughout the day and you might find you are more prone to succumbing to minor ailments, like colds etc as your body may not have sufficient 'fuel' at any one time to fight things off. Most nutritionists recommend that you eat small meals, frequently, about every four hours or so. Apparently, if you leave it too long between meals, your body can feel 'starved' and will concentrate on 'feeding' your vital organs, rather than 'non-essentials' like your skin and hair. So you could find that the condition of your skin and hair suffers. A few months ago, my boyfriend slipped into the habit of skipping breakfast and lunch and just eating a meal in the evening. After a month or so of this, he did start to feel tired, yet he couldn't sleep at night. He was also pretty grumpy! He's now eating regularly again and feeling much brighter. If you're not eating much during the day because you simply don't feel hungry, then do try and eat something little and you will probably find that your appetite increases naturally.