There is no starvation level of calories. There's a starvation level of nutrients. The way calories come into play is that it's impossible to get nutrients without food, and the minimum amount of food the average young adult male would need to get those nutrients would probably have 1700+ calories.
People don't gain weight from eating too little. That's a myth. Under certain circumstances, people who eat too little and are therefore undernourished will maintain their weight for a long time, but not gain. And even that effect takes a while to start.
Explain what you mean by "sudden gain of weight." It sounds like you're talking about something that happened over the span of a day-- is that right? Remember that food has weight unrelated to its calorie content. If you get on the scale after eating something, it's the same as getting on the scale holding that food in your hand. The weight of the food is added to yours because you're holding it, but it's not part of your body.
In your case, If you've suddenly started gardening, I'm betting that you also drank a lot of water. (At least I hope you did!) Water is very heavy, but has zero calories. "A pint's a pound the world around"-- every two cups of water weighs one pound. If you get on the scale after drinking a liter of water, the scale will show an extra two pounds, but that's just from the water you're holding. As soon as it works its way through you, your weight will return to normal, just the way it would if you got on the scale with a water bottle in your hand and then set it down on the counter.
Now, that doesn't mean that 1700 calories is enough. If you're walking 12 miles and doing 4 hours of yard work, you'll need to eat more or you'll start to feel sick. But it's not going to cause weight gain.
| current weight: 132.0