Why have I hit a plateau?

Well, I don't know why you've hit a plateau. It may be that you've stopped monitoring your diet. It may be that you're slacking on your exercise. I'm going to suggest another reason that you don't often read in diet book. It's this: Plateaus are natural and to be expected if you follow a static diet and exercise plan!

Read the example I came up with predicting my own weight loss. Based on the equations governing metabolism and weight loss, I predicted a plateau for my weight loss before I dieted!

My Plateau

Consider my case. When I started my diet and exercise program, I was a 5'4", 140 lb, 43 year old woman. My weight was pretty stable, meaning I was not gaining or losing weight as far as I could tell. I was doing no formal exercise, and my day consisted of light office work. I wanted to lose 10 lb.

At 140 lb., I estimated my daily calorie expenditure to be 1785 Calories/day. I knew I would need to eat less (or exercise more) at 130 lb.. So, I ran program and found that if I continued with my currently activity level my calorie expenditure would be 1726 Calories/day. Yes, I would need to eat 54 Calories less each day! That's about 1/2 a slice of bread! While I was at it, I decided to calculate something I call a "weight factor" ; this is the number of calories associated with gaining or losing exactly 1 lb. For me, it's 5.4 Cal/day/lb.

Ok, I was psyched now! After I finish my diet, to keep my weight off, all I would have to do was to eat 54 Calories less a day. WOW!

So, could I do it? I observed myself over the next few weeks, and I realized: I buy a candy bar and immediately eat it every time I go to the grocery store. EVERY time. I go to the grocery store about 3 times a week. I flipped over the candy bars and read the nutrition label: that's about 250 calories/bar * 3 bars/week / 7 days a week = 107 calories a day! The candy bars represented more than the extra calories I needed to cut from my diet. So, if I could just stop eating them without compensating by eating more, I'd lose the 10 lb. I wanted to lose and then some. I figured: yes, I could change my habits to keep of the weight forever!

Of course, I wasn't stupid enough to think I'd lose the weight the instant I stopped eating my first candy bar. But I was curious. I asked myself: if I just stop eating the candy bars, how long before I reach my target weight?

Being the mathematical sort, I looked up some facts to develop a theoretical prediction of my weight loss. These are the facts I used for my theoretical model:

I will lose 1 lb of fat when I burn 3500 more calories than I eat.
My metabolic rate will drop 5.4 Calories/day every time I lose a lb.
I'll assume I just stop eating the 250 calorie candy bars 3 times a week, and otherwise don't change my diet or exercise level at all!

I calculated how much weight I would have lost as a function of time after I stopped eating the candy bars. That would create a deficit of 1000 calories a week. I made this graph; the green curve called "average metabolism" is my best prediction of my weight loss over time. Look, the theory predicts a plateau!

Examining the graph I learned a few things.

According to the equations, I would eventually lose about 20 lb. if I just stopped eating the extra 750 calories a week in those 3 candy bars. The weight loss of 20 lb. is indicated by the blue line which I called "plateau". Notice the green line bends over. As my weight loss approaches 20 lb., it slows down and stops.
It would take me 4 1/2 weeks to lose the first pound. This is agrees with the advice "you'll lose 1 lb for every 3500 calories deficit." you hear in all the diet book.
It would take me 15 months to lose the 10 lb.
It would take me forever to lose 20 lb -- assuming I want to lose 20 lb!

I did a little more investigation and learned that experiments show that women of similar heights and weights can have different metabolic rates. So, I estimated a high metabolic rate "weight factor" and a "low metabolic rate" weight factor. Then I repeated my weight loss analysis. The results for the high and low metabolism are illustrated with yellow and magenta curves respectively. I found:

If my metabolism is actually higher than most women of my height and weight, my predicted weight loss would follow the yellow "high metabolism" line. I'd initially lose at the same rate as a woman with an average metabolism, but lose less total weight. (This may seem strange, but it's true. People with a high metabolism need to eat more calories to sustain the same weight as someone with a lower metabolism. They also need to cut more calories to lose the same amount of weight. If I did have a high metabolism, it means I was previously eating closer 2142 Cal/day instead of 1785 Cal/day. If you still think it makes no sense, think of it the other way around. If I started eating 3 candy bars a day, I wouldn't gain as much weight as someone with a slow metabolism! )
If my metabolism is slower than most women my height and weight, I would lose more total weight. My predicted weight loss if I have a low metabolism is shown with the magenta line.

I'll tell you how I used this information to set up my diet and exercise plan, but first I'll return to talk about the question on the top of this page:

Why has your weight hit a plateau?

Well, when you started your diet and exercise program you probably decided to cut a specific number of calories from your diet, or to exercise to burn a specific number of calories-- or some combination of the two. But the key is, you said something like: "I'll cut out 250 calories a day, then I'll lose one lb every two weeks." Well, notice that the theory predicting your weight loss says you will lose one lb every two weeks initially. Eventually, you'll lose weight more and more slowly until you've hit your plateau. Why? Because you weigh less. It now takes fewer calories to sustain your weight! You will hit a plateau. Everyone will!

If you've lost a lot of weight, but you've hit a plateau you should:

make sure your diet provides at least 1200 calories a day. If it doesn't, you metabolism may have slowed down. I'm not going to discuss that, but that would make it impossible to predict your weight loss rate.
verify that you really are following your target calorie consumption plan. Spend a week measuring all food carefully and writing down everything you eat.
verify that you really are exercising to burn the number of calories you planned. Write down the duration and intensity of each exercise session.
reassess figure out if you've actually hit the theoretical plateau!

If you've hit your theoretical plateau, the only possible ways to lose more weight is to create an even larger calorie deficit. Yep, either eat less or exercise more. Before you do that, do ask yourself: "Is losing more weight worth it?" It may very well be that you've lost enough weight for now!

How I used my analysis!

Well, I decided that I wanted to lose my 10 lb. in less than 11 months. I wanted to be able to lose between 1/2 and 1 lb a week. That means I needed a deficit of at least 1700 calories to 3500 calories a week. The three candy bars represented 750 calories a week. I decided I would try to exercise enough to burn at least 1000 calories a week. If you want to read details showing my plan, and how I implemented it, visit "My First 12 Week Diet and Exercise Plan".

Lucia