Juliette and I were out on a long ride yesterday joking about how we were burning more calories than we would eat that day. To pass the time we were trying to figure out our mileage rating like you do for cars. We finally came up with a rough estimate of 3 km/fig newton.

While we were doing these calorie calculations in our heads, we passed a sign that said 30 lbs, 30 days, $30. It sounds reasonable enough, loose only one pound a day, but it gave me something to work out over the next few kilometers of our ride.

I think that most people would agree that to lose weight, you need to be burning more calories than you take in. If you eat too much, most of the excess is turned into fat and stored. If you eat too little, your body starts raiding those stores, burning the glycogen (sugar) stored in your muscles and the fat stored in all of those unsightly places. The only other way to lose weight is through dehydration, but that is only temporary.

So, beginning there, I started making the calculations in my head.

• To lose 30 pounds in 30 days, you would need to burn one pound of fat a day.
• 1 lb = 455 grams, so you would have to burn 455 grams of fat each day.
• 1 gram of fat = 9 calories, so you would have to burn 4095 calories each day.
• The recommended calorie intake for women is about 1940 calories per day and 2550 for men. If you want to figure it out for yourself, there are plenty of calorie calculators available on the Internet.
• The recommended calorie intake is based on what your body requires in a given day.
• Therefore, if you do not change your activity level for a given day, and ate nothing, you would only burn 1940 to 2550 calories per day (or .47 to .62 pounds of fat.) This assumes that you could eat nothing for 30 days.
• To burn the remaining 1545 to 2155 calories, you would need to increase your activity accordingly.
• Moderate biking burns between 500 and 700 calories per hour.
• Therefore, you would need to add to your daily routine 3 hours of moderate biking every day while not eating anything for 30 days!

So, 30 pounds in 30 days is obviously a scam, but they must get some results, so how do they do it? The answer is simple, go back to the second way I mentioned for losing weight, water. One litre of water weighs 2.2 pounds. I think you would feel pretty awful if you were dehydrated 13.6 litres, but I guess that it is possible over 30 days, especially if you are more than 30 lbs overweight. Maybe they mix that with drugs like speed that would make you burn more calories, but that doesn’t seem to mix with the $30 bit.

Does anyone have experience with these diets who wants to fill us in on how they work? Please leave comments if you do.