Does the Speed of Dieting Affect Weight Regain

The concept of slow or fast dieting does not refer to how fast one eats, rather to the rate to which one loses weight from dieting. There is the more traditional thought if you can lose weight more slowly (a slow diet), you can keep it off more successfully that if you lose weight too quickly (a fast diet).

However, proponents of “fast dieting” are now challenging this theory, claiming it is actually better than “slow dieting” for preventing weight regain after weight loss.

“Fast Diet” Research in Athletes

The “fast diet” appears to be gaining the most traction in the fitness and body building worlds – hinging the argument on two studies from a group of Norwegian sports scientists in 2011.^3,4 

High-level, Olympic caliber athletes were randomly assigned to either a slow-diet or fast-diet weight loss rate groups through caloric restriction (eating less), while they continued strength training.

On average between the two studies:

Both groups lost about 5% of their body weight by cutting calories (mostly fat), but the slow-diet group lost it in 8.6 weeks, while the fast-diet group lost it in 5.6 weeks by cutting one to two hundred or so more calories per day. Despite similar weight loss, the fast-diet actually showed reduction in several performance variables, such as maximum strength, while the slow-diet had no change.

However, it was the second study⁴ that likely created the revised promotion of “fast-dieting,” but perhaps a bit prematurely at this point.

After both groups lost the same amount of weight during the intervention, they were re-tested 6-months later. They found that the slow-diet group had gained back much of the weight they lost, while the fast-diet group only gained back a little. Clearly, the fast diet worked, and prevented weigh regain, right? Well, let’s look at a few things.

First, see how large or long these error bars are? If converted to standard deviation, which represents the average distance from the mean, at 6 months, it was ± 6%. So, athletes could have gained all their weight back or lost an additional 6%, on average. Odds are, they did not lose 12% of their body weight, so what likely happened, was several athletes regained more weight back, but a few others maintained weight loss or lost a little more, thus keeping the mean lower at around 5%.

So, we can then conclude that with such a small sample size (9 athletes), there appears to be large variation in how individual athletes’ weight will respond or rebound to fast-dieting, which cautions promoting fast-dieting as a for sure, effective prescription for everyone.

Yet, the kicker occurred at 12-months, where the athletes were tested, again. Both groups gained the weight back. In other words, neither slow- or fast-dieting actually helped the athlete maintain their weight loss.

“Fast Diet” Research in Non-Athletes

Now, these studies, although well done, looked at a handful of high-caliber, Olympic level athletes, who arguably have a strong handle on their dietary self-control and restriction. Also, both slow- and fast-dieting groups were in a normal range of safe, healthy weight loss. So, it was not really that fast or some rapid, crash diet.

Also, the potential myth surrounding the rate at which one loses weight likely originated with non-athletes, so the next question is what effect do fast diets have in this population?

Two more recent studies answer this question.

This study⁸ had 57 adults classified as overweight to obese randomized to two groups: a low-calorie diet of 1250 kcal/day for 12 weeks (the slow-diet group), or a very low calorie diet of 500 kcal/day for 5 weeks (the fast-diet group). By the end of the study, both groups had lost around 8-9 kg (17-20 lbs). However, by the 9-month follow-up, both groups had regained the same amount of weight back.

This larger study found the same thing, that despite fast- or slow-dieting, the weight regain was the same.⁶

Thus, “speed of dieting,” again, did not differentially impact weight re-gain. Rather, as shown in these scatter plots, those who lost more muscle mass or maintained less physical activity tended to gain back more weight. And, the fast-dieting group tended to lose more muscle mass.

Even other studies support the important role of maintaining physical activity (as little as 80 minutes per week), weight training, and muscle mass for prevention of weight regain.^1,2,5,7

There are also the numerous psychological factors that affect weight loss maintenance, such as weight cycling, disinhibited eating, eating in response to negative emotions and stress, more passive reactions to problems, self-monitoring, dietary consistency, confidence, internal motivation, autonomy, assuming responsibility, and self-control.²

In conclusion, weight loss maintenance is elusive for many. There are several known factors that do contribute, but there are still mysteries to be uncovered. For now, however, the current research does not support that fast-dieting, or slow-dieting for that matter, have an effect on preventing weight re-gain. Rather, fast-dieting could pose further challenges through loss of muscle mass and decreases in performance.

References

1. Curioni, C. C., & Lourenco, P. M. (2005). Long-term weight loss after diet and exercise: a systematic review. International Journal of Obesity, 29(10), 1168.
2. Elfhag, K., & Rössner, S. (2005). Who succeeds in maintaining weight loss? A conceptual review of factors associated with weight loss maintenance and weight regain. Obesity Reviews, 6(1), 67-85.
3. Garthe, I., Raastad, T., Refsnes, P. E., Koivisto, A., & Sundgot-Borgen, J. (2011a). Effect of two different weight-loss rates on body composition and strength and power-related performance in elite athletes. International Journal of Sport Nutrition and Exercise Metabolism, 21(2), 97-104.
4. Garthe, I., Raastad, T., & Sundgot-Borgen, J. (2011b). Long-term effect of weight loss on body composition and performance in elite athletes. International journal of sport nutrition and exercise metabolism, 21(5), 426-435.
5. Hunter, G. R., Brock, D. W., Byrne, N. M., Chandler‐Laney, P. C., Corral, P., & Gower, B. A. (2010). Exercise training prevents regain of visceral fat for 1 year following weight loss. Obesity, 18(4), 690-695.
6. Purcell, K., Sumithran, P., Prendergast, L. A., Bouniu, C. J., Delbridge, E., & Proietto, J. (2014). The effect of rate of weight loss on long-term weight management: a randomised controlled trial. The Lancet Diabetes & Endocrinology, 2(12), 954-962.
7. Swift, D. L., Johannsen, N. M., Lavie, C. J., Earnest, C. P., & Church, T. S. (2014). The role of exercise and physical activity in weight loss and maintenance. Progress in Cardiovascular Diseases, 56(4), 441-447.
8. Vink, R. G., Roumans, N. J., Arkenbosch, L. A., Mariman, E., & van Baak, M. A. (2016). The effect of rate of weight loss on long‐term weight regain in adults with overweight and obesity. Obesity, 24(2), 321-327.