Answer: too easy
Granted, the following is a fictitious example but it’s done for illustration purposes. If I keep my moderate activity level and burn off 2500 calories per day, and it takes approximately 3500 extra calories to store one pound of fat (assuming all extra calories go to fat storage), I’d need to eat 6000 calories a day to gain one pound of fat. In 10 days of doing this I’d gain 10 pounds of fat.
This is a sample “day” but obviously there can be more variety totaling the same amount. Other than making yourself sick, you will also retain a lot of water weight given the extra salt.
McDonald’s: 3 Big Macs = 1620 calories
Wendy’s: 3 Large Orders Natural Cut Fries = 1560 calories
7 Good Humor Ice Cream Sandwiches, Vanilla = 963 calories
Peanut Butter M&M’s, 12.7 oz. package (Medium) = 1870 calories
Total: 6013 calories
If I did this for 10 days I’d gain approximately 10 pounds of fat. An important point, however, is that fat is rarely gained in consecutive days (unless you’re on a long vacation, you’re Morgan Spurlock in Supersize Me, or a competitive athlete rebounding from a very low body fat level). In most cases, fat weight is gradually increased over time. A birthday here, holiday there, company dinner, etc. Unless you’re actively counterbalancing these occasions with days of significant deficits, you may wonder how it happened or fall into the excuse of, “I’m just getting old.”
On the bright side, it’s never too late to steer things in your favor.