For anybody who is losing weight aggressively, there is always a problem lingering in his/her mind. Could something go wrong if the weight loss goes too fast?

This is a legitimate question. Besides exercise injuries and minor side effects of low calorie diet such as diarrhea and heart burn, there is another complication which is less common but also real. Studies have consistently found that those who lose weight rapidly using extreme low calorie diet may be in a higher risk of developing gallbladder stones. In a pooled analysis of several small weight loss programs, the authors found that weight loss is related to the risk of developing gallbladder stones in an exponential curve fashion with the threshold at 1.5 kg per week (3.3 pounds per week). The incident rate is 5 per 1,000 at 1.5 kg weight loss per week, while it is about 1.7 per 1,000 at 2 kg (4.4 pounds) per week, a triple increase of risk. It seems I am lucky that I hadn’t had symptomatic gallbladder stones during my aggressive weight loss. Thank goodness!

Millions of years of evolution have set up the human body to conserve energy. In periods of starvation such as famine season or modern dieting, the body will lower the energy expenditure and increase the use of fat. The liver is the major organ in converting fat to glucose. It has shown that during starvation, the liver also generates more cholesterol from fat than usual. The cholesterol over-saturation in bile (secreted by the liver) may facilitate the formation of gallbladder stones.

A recent study has also pointed to another situation. That is, those who have yo-yo weight are also in danger of having gallbladder stones. Yo-yo weight, the weight cycle, is very common for people who have tried weight loss, simply because it is very hard to maintain the new lifestyle. Some people return where they were in a couple months, and many even become heavier than before weight loss. Even worse, the proportion of fat mass may be higher than before because the body tends to regain more fat mass than lean mass during a fast weight gain. Therefore, the liver may also generate more cholesterol, thus increasing the risk of developing gallbladder stones.

In the study that examined the incidence of symptomatic gallbladder stone disease among weight cyclers compared with weight maintainers, those who had the most severe weight cycle (losing 20 lb or more weight and regaining similar amount of weight) had the highest risk of developing gallbladder stones (42% more likely than weight maintainers did). There is a dose-response effect between weight cycle and gallbladder stone disease: the more severe weight cycling, the more likely to have gallbladder stones. This effect is independent of body mass index (which measures the overall body fatness), age, dietary factors, and other confounders. In summary, the danger is real.

On the other hand, among severe weight cyclers, the incident rate of gallbladder stone disease is 6.4 per 1,000 person years (py), while the incident rate among weight maintainers is 4.2 per 1,000 py. Therefore, although the relative risk is higher for severe weight cyclers (1.42 times more than the weight maintainers), the absolute risk difference between them is only 2 per 1,000 py. From this point of view, the risk is not big anyway.

I have lost more than 20 pounds during the last two months, what the actual risk of having gallbladder stones in my own situation? Since I lost almost 4 pound per week, the risk of having gallbladder stones is about 1 per 100. Apparently, I haven’t gotten symptomatic gallbladder stones yet (but it is possible there are little stones inside my gallbladder already). If I do regain the same weight in the next few months, the risk of having gallbladder stone will be 6.4 per 1,000 py.

In addition, it is well known that obesity is a major risk of developing gallbladder stone, and those who have BMI more than 30 kg/m^2 are twice as likely to develop the disease as those with BMI less than 25 kg/m^2. Given that I have already lost quite a lot of fat, the absolute risk of having gallbladder stones now is lower than when I was 2 months ago.

It is also documented that exercise can reduce the risk of gallbladder stone formation. Since my weight loss program contains regular exercise, the exercise may counteract the side effect of low calorie diet in forming gallbladder stones.

Dietary factors may also prevent forming gallbladder stones in bile. For example, fibers and vitamin C (that is, more fruit and vegetables and less meat) may help reduce the risk.

Furthermore, if I keep on exercising and restricting my diet somewhat, the stabilized weight will reduce the cholesterol secretion by the liver, and the possibly formed small gallbladder stones may be self-dissolved.

Those who have suffered gallbladder stone disease can testify the extreme pain and torture of the disease. Sometimes you need to go through surgeries to remove the stones. Nevertheless, gallbladder stone disease is not the end of world, and this small risk must be outweighed by the greater benefits of weight loss. Just be cautious.