Step 1: Slow down your metabolism
The very first thing you've got to do is slow your metabolism; by slowing your metabolism you'll burn fewer calories when you're at rest and thus, even if you don't increase the amount of food you intake, you'll automatically add weight and store body fat. The easiest way to slow your metabolism is to stop all forms of exercise. Avoid walking. Spend a lot of time in front of the television. Take elevators instead of the stairs.

Some of the best strategies for lowering your metabolism include getting a desk job, finding parking spaces as close as possible to the stores where you shop so you don't spend much time walking across the parking lot.

Avoiding physical exercise has a second effect -- it also causes your body to break down the existing muscle mass that you have today. And by breaking down muscle mass, your metabolism will be slowed even further. This will accelerate your weight gain efforts and allow you to pack on the pounds almost automatically. The quickest way to get rid of the muscles that you don't want is to simply stop using them, and your body will take care of the rest.

Step 2: Drink carbonated soft drinks
One of the very first things you should do is get yourself addicted to caffeinated soft drinks. You can start by purchasing a 12-pack of any soft drink beverage in grocery stores and consuming it at every possible opportunity, including breakfast. This is an absolutely wonderful way to pack on the pounds, because soft drinks are made with high-fructose corn syrup.

When this ingredient is consumed, it spikes the blood sugar in your body. This sends an emergency signal to your pancreas, which produces increased levels of insulin in order to keep the blood sugar levels from going too high. This insulin signal is picked up by the cells in your body, which then remove blood sugar from your bloodstream and, through a somewhat complex biological process involving the liver, manage to store that blood sugar as body fat. If you drink enough soft drinks with enough frequency, you will be well on your way to achieving your goal of gaining 100 lb in 12 months or less.

Step 3: Choose rich caloric dense foods
While you're at it, be sure to purchase foods with very high caloric density. Raw, uncooked fruits and vegetables will fill you up before you get very many calories in your meal. For example, it's very difficult to eat 1,000 calories worth of apples at one sitting. Your stomach will simply fill up before you reach 1,000 calories and you won't feel like eating any more. But if you choose processed foods with ingredients such as white flour, hydrogenated oils or saturated fats, you can pack in a couple of thousand calories in one sitting without topping off your stomach. This is hugely important for achieving your weight gain goals.
Fortunately there are a great number of foods available at every grocery store in America that can help you accomplish this. It's very easy to buy them, as most are quite affordable. All you have to do is look for brand-name foods packaged in beautiful boxes with delicious-looking pictures of foods on the front.

Step 4: Gallop junk foods
Junk foods are, of course, another outstanding choice for achieving your goals. A bag of potato chips provides an impressive quantity of dietary fats as well as refined carbohydrates - and various nacho chips and other snack foods operate in much the same way. You can also accelerate your weight gain goals by turning to fried foods.

Step 5: Increase the number of visits to fast food restaurants
If you had to name an ideal source for the combination of food ingredients that would rapidly accelerate your quest for obesity, you'd have to put fast food restaurants at the top of that list. The more popular the fast food chain, the faster their food packs on the body fat, it seems. (Maybe that's what the "fast" in "fast food" really means...)