We have received much positive feedback regarding intermittent fasting over the past few months. People have taken the basic premise of a high quality paleo/Zone diet and either compressed their feeding schedule or, in a few cases, adopted an alternate day fast with good success. What type of success? People have reported fat loss, muscle gain, improvements on CrossFit diagnostic WODs and increases in 1 rep max strength efforts. Keep in mind that the people reporting these results are not new trainees but rather athletes at or near the top of their game. That’s all pretty nifty, but no matter how good something is there is usually a population that is ill-suited for a given protocol. Could that be the case with intermittent fasting? Well, I think there are a few situations that certainly warrant some caution when implementing IF.


Clinically Obese

Ironically the population that might benefit the most from IF is a group that really needs to be cautious with implementation. Overweight individuals are by definition insulin resistant. This peridiabetic condition lends itself to severe blood sugar crashes when feedings are not consistent. Thus these individuals must eat every 2-3 hours or face severe mood swings, lethargy and for some the difficult to remedy condition of DEATH. Why? Severe insulin resistance can prevent the facilitated diffusion of ketones through membranes such as the blood-brain barrier. This can lead the condition ketoacidosis which is often characterized by both high blood glucose and high blood ketone concentrations. This can lead to a low blood pH… and that can be very bad. What to do? Reestablish euglycemia by implementing a paleo/Zone or cyclic low carb diet. As insulin sensitivity is reestablished brief fasts should be both safe and therapeutic. Keep in mind that insulin resistance has two major contributors. The first is chronically high insulin levels which tend to down regulate the number of insulin receptors. The second factor involves damage to the insulin receptors themselves via non-enzyme mediated glycation due to chronically high blood glucose levels. Individuals with hyperinsulinism not only have fewer insulin receptors but the few they have are in effect broken. That considered, a therapeutic fast could be one of the most effective means of re-establishing insulin sensitivity; however, if the pathology is of sufficient magnitude, ketoacidosis and The Big Nap could occur.


Clinically Busy

With regards to life extension and disease amelioration, caloric restriction and intermittent fasting appear to work via mechanisms in which acute stressors increase the expression of heat shock protein genes (HSPs) and modulate immune function favorably. Sounds good so far, but the key term in the previous sentence is “Acute Stressors”. What happens when an otherwise favorable stressor becomes chronic and overwhelms our adaptive ability? The short answer is “Bad Things”. Let's look at IF like it’s a drug. Drugs have physiologic effects, characteristic dose/response curves and therapeutic ranges. Dose response curves represent what level of physiologic response can be expected for a given dose. For example, how much pain relief one garners from a given dose of aspirin. The therapeutic range is the approximate amount of drug that may be administered and, in general, deliver a beneficial effect. Below the range one experiences little or no effect, and above the range we have too much collateral damage—also called Side Effects. In ideal situations a drug provides benefit at fairly low doses and negative side effects are not experienced until much higher doses. The reality is that most drugs have a fairly narrow window and interestingly things like age, sleep, general health and stress can greatly affect this therapeutic window. As with drugs, so too with intermittent fasting. Some can go a long way. If you are really sick you may need a lot more (remember last month when Dr Seyfried talked about ketogenic diets, fasting and cancer? One might elect to take a much larger IF dose if one is dealing with cancer than if one is simply looking to improve performance). If you are chronically besieged by other stressors, ANY dose of drug (or IF) may be too much. How are you to know? We should have an expectation of intermittent fasting improving body composition and performance. These are immediate, measurable effects. Assuming one starts IF and things go favorably initially but then say one gains a layer of fat about the midsection, sleep is disturbed or performance slumps it may be prudent to alter your dose in some way. That may mean a smaller dose (12 hour fasts instead of 18), fewer doses (every 3 days instead of every 2) or maybe you need the anti-stress effects of a very consistent Zone diet. If your life is VERY complicated and stressful it may be too much to add any type of IF to the mix. Always keep in mind that a surefire way to ruin your health and athleticism is to not eat sufficiently during an intermittent fasting protocol. Don’t do it. You won’t like it.


Medicated

In addition to the situations I described above remember that Dr. Seyfried (http://www.performancemenu.com/backissues/index.php?show=issue&issueNum=18&PHPSESSID=8634181c6966973baf5746f8846299bf) mentioned extended fasts can alter liver metabolism and thus alter clearance rates of drugs. If you are heavily medicated (I wish I were right now), seek medical advice before jumping into this.