With regard to hair loss this is a known side effect of very low calorie dieting. The reason this happens is that the hair root is one of the most active sites in the body in terms of new cells being produced. Hair grows in three stages. The very active phase (anagen) when new hair cells in the hair root are being produced and the hair shaft is growing. Then there is a resting phase (catagen) when there is little cell division in the hair root and the hair shaft is not growing. The base of the hair disconnects from the root and just rests in the follicle. Then there is the telogen phase when the hair sheds because the hair root has gone back into the anagen phase ie growing again, the cycle is starting again,. with the new hair pushing out the old. There are millions of hair follicles in the body. At any one time most follicles are in anagen around 3% are in catagen and around 11-15% are in telogen. Because anagen takes up a lot of energy when energy balance ie calories are reduced, anagen is the preferred process for the body to shut down. Therefore more follicles go from anagen into catagen than would normally be the case about 18-20% although the exact proportion is different for everyone. When energy intake eventually increases these same follicles go from catagen into telogen and the hair in them is shed. This means that for anyone who is on a diet there are more hairs being shed than normal but this usually remains unnoticeable. However in about 4% of people the proportion of follicles in telogen exceeds 30% and this is when the hair loss becomes noticeable (the condition is called effluvium) it is more likely to be experienced by people who have experienced hair shedding in the past eg following a pregnancy, stress etc. Once energy intake is increased the proportion of follicles in the different phases goes back to normal and hair growth proceeds as normal. Hair shedding due to calorie restriction is a temporary condition and it indicates the growth of new hair. If there is reduced energy supply our bodies will react to prioritise vital functions, how this happens is a very individual response but unfortunately for some people it will present with hair shedding which can be very distressing. While on a very low calorie diet no two people will be identical as to when hair starts to shed and when new growth will commence it will depend on the individual. As a natural adaptive response there is not much that can be done to resolve the problem other than waiting for the cycle to complete, which we cannot be definitive about as the amount of hair that is the resting phase at any one time for an individual will be unknown.
Once calorie intake is increased, hair will start to grow in the follicle, for this process to complete this can take 3 months or more exactly how long this will take to complete we are unable to say, and we do appreciate that it is a very distressing situation but unfortunately it can be a known side effect of very low calorie dieting, irrespective of the particular diet programme chosen.