Fasting Side Effect 2: Weight loss

With regards to weight loss and fasting, people generally fall into two groups -

1. Those who are already very health conscious and want to enhance their health further,

and

2. Those who may have previously neglected their health and would like to try fasting as a method for helping them return to good health.

Both are good reasons to engage in fasting. Not surprisingly, since nearly 2/3rds of Americans are now overweight or obese, people who are visiting this website probably fall into the second group. If you are among these people then maybe you are hoping that fasting will act as an effective method for achieving weight loss. That’s okay and fully discussed in our guidelines. However, for those already on the low end of their normal body weight, or are underweight, weight loss as a side effect of fasting for other reasons (rather than a goal) can be unsettling. This can especially be true in the case of body builders or the athlete who seeks to retain muscle mass.

Our recommendation is essentially a compromise. We suggest that if weight loss is an unwanted concern, especially the loss of lean tissue (organ or muscle) then you must limit your fasts to no more than 72 hours. The evidence is not exactly clear on this but it suggests that initially, your body will use its current carbohydrate supply first, dip into fat stores second, and THEN start to use muscle, connective tissue, and organs. But it's not as simple as first, second, and last.

For instance, in the first 24 hours of a fast, it may be 40% carbohydrate/60% fat. Then, over the next 24 hours, it gradually shifts towards a ratio closer to 5% carbohydrate consumption, 93% fat utilization, and 2% lean tissue self-digestion. Then, in the next 24 hours, your body MAY shift as far as 0% carbohydrate utilization, (because it is all gone at this point), 95% fat consumption, and 5% lean tissue self-digestion. Your body may settle into this ratio for the remainder of the fast. For others a different steady state balance between the three sources may occur.

The truth is that everybody is different and no consensus has been reached regarding these figures. More research is needed to establish reliable averages. If your body is lean to begin with, the best estimate is 72 hours before lean tissue starts to become digested at a significant quantity.

The concept we are essentially discussing is that of "biochemical individuality". This means that while all human cells need glucose and all humans are capable of creating an intrinsic supply of glucose through gluconeogenesis (in the liver), we all do this to varying degrees and balance our glucose levels with varying levels of insulin depending on our individual supplies and genetic variability. From a physiologic standpoint, what may be absolutely normal for one person may not be for someone else.

All of the RDA's (recommended daily allowances) you see on the side of food labeling are really just an educated guess based on statistical models among populations. They’re ultimately the best guess we can make based on research that’s been sanctioned by the US government to help us all understand our nutritional needs.

In fasting, the same concept applies - you (along with your physician) must be willing to become a student of your body. You will be making careful observations, as well as taking physical and chemical measurements to maximize your results and make them as long lasting as possible, hopefully even permanent. If you are not engaged in a supervised fasting (and not everyone needs to), and weight loss is a concern for you please limit your fasts to 72 hours in duration. Your doctor can safely take measurements regularly with percent body fat and percent lean tissue to see what's happening to your body over time.