According to the American College of Sports Medicine guidelines it is safe and appropriate to lose up to 1 kg (2.2 lbs) per week. This value, unto itself, is not completely unreasonable. The guideline was established to help weight loss participants manage fat loss without decreasing lean mass. In theory two (2) pounds a week does not seem like an inordinate amount of weight, especially when you consider the weight loss claims and advertisements regularly appearing on television, in magazines, and on the web. It is not uncommon for companies to suggest they can help you lose ten pounds of weight in one week. But when thought process leaves fantasy land and looks at evidence-based science the two and ten pound weight loss numbers become somewhat unrealistic. Consider what it actually takes to use the equivalent energy of 10 pounds of fat. At 3500 kcals per pound ten pounds of fat is equal in energy to 35,000 kcal. The average person burns 100 kcal running one mile. So to lose the ten pounds in one week a person would have to run 350 miles or 50 miles per day, essentially running further than the distance from Philadelphia to Boston every week. That of course is assuming the same person maintains a neutral caloric balance prior to the exercise. It is probably safe to say 10 pounds of weight loss from adipose tissue in one week is nothing short of laughable. People who actually lose notable quantities of weight in one week are actually losing water, not fat. If dehydration is your goal simply stop eating carbohydrates and you’ll lose 6-7 pounds in a week from metabolic water loss alone.

It would seem that ten pounds is obviously out of the question, but what about the two (2) pound weight loss guideline? Is that reasonable? Once again to answer this question you must go back to the numbers. Two pounds of fat weight is equivalent to 7000 kcals or 70 miles of running per week. So ask yourself this question, is it reasonable to expect someone to run ten miles per day everyday of the week and at the same time consume a neutral caloric balance before the exercise is even factored in? By now it should seem fairly obvious that two pounds of fat holds a significant amount of energy. Considering the average person has the physical conditioning to expend about 200-300 kcal per workout (2.5-3.75 miles walking or 2-3 miles running) it would be safe to say that two pounds of weight loss from exercise alone would take about a month (28 days) if exercise was performed every day. Now consider a person who exercises two or three times a week for 30 minutes as advertised on many TV commercials as all it takes to lose inches using their fitness equipment. At this frequency it would only take 3 months (12 weeks) to lose the two pounds, again assuming neutral caloric balance without the exercise factored in. Everyone knows exercise is extremely important to weight loss but it seems obvious dietary constraint needs to be included for successful fat loss over a reasonable period of time.

Let’s analyze this from the other perspective of energy balance, calorie control. If a person decided to attempt the two pound weight loss in one week using diet alone, they would have to create a negative caloric balance of 1000 calories per day. This suggests that the person would already be consuming a neutral caloric balance before the 1000 calories were removed. To figure out what it would take to establish a neutral caloric value we need to calculate daily need. Using the average male anthropometric measurements you would have a 5’10”, 174 lb. male with a body composition of 18%. His estimated resting metabolic rate would be 1770 kcal (lean mass formula), and assuming his physical activity was that of the normal American his daily need would be 2479 kcal per day (1.4 multiplier). So to lose the two pounds of fat this individual would need to reduce his caloric intake to 1479 kcal. Most men will eat this quantity of calories in a standard restaurant served lunch. A major problem facing fitness professionals is that the average person is not consuming a neutral caloric balance. The average male consumes around 3000 kcal per day. So the first step would be establishing the neutral caloric balance, in this case reducing intake by 531 kcal in addition to the 1000 kcal reduction to create the negative caloric balance necessary to attain the two pounds of weight loss. Once again this is not realistic. Expecting a person to reduce their caloric intake by 51% is comparable to expecting them to run 10 miles a day.

It should be clear by now that two pounds of weight loss per week is an unattainable goal for the majority of the population. So what is reasonable? People need to succeed at small adjustments rather than fail at large ones. Expecting someone to burn 750 kcal a week from exercise related activity is reasonable, as is reducing daily caloric intake by 250 kcal a day. If this combination is used routinely it would take about 10 days to lose a pound, or two pounds about every three weeks, assuming the diet was neutral from the start. If the diet was in positive balance at the start of the weight loss program it would take much longer to lose the weight if it would occur at all (depends on the positive calorie value). Consistent effort towards small changes adds up over time. If the same person actually made lifestyle changes rather than acute adjustments common with dieting they would have significant weight loss over a year’s time. In the example the individual would have a negative balance of 357 calories per day which over a year equates to 130,305 kcal, or 37 lbs of fat energy. Taking a large number of small steps will get you much further than taking a few big steps.