Science Says Crash Diets Work Best For Long-term Weight Loss

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But if you don’t do these three things you're unlikely to keep it off

If you're looking to lose weight and to keep it off, you've no doubt been told to avoid crash dieting. Often The Biggest Loser is cited as the worst example to follow. We all know that the contestants mostly put all their weight back on, and more, right?

Wrong.

What research shows works best is what you've been told not to do. A study just published (March, 2020) confirms yet again that a large rapid rate loss is the best predictor of the long term ability to maintain weight loss.

Let's start with The Biggest Loser. Here's a typical reference to it and the associated advice to go slow. From the Fitbit Blog:

The recent Biggest Loser study, although an extreme example, shows how losing weight too quickly can really mess with your metabolism. By eating too few calories, you push your body into conservation mode, slowing down natural processes to save energy. The trick to healthy calorie cutting? Do it slowly and don't go below your resting metabolic needs—slow and steady weight loss wins the race. ​

I clicked through and read the Biggest Loser Study ("Persistent metabolic adaptation 6 years after "The Biggest Loser" competition"). You might be as surprised as I was to find that the researchers concluded exactly the opposite of the advice given above.

Contestants were more successful than average in keeping weight off

In the first place, the study concluded that The Biggest Loser contestants were more successful in keeping their weight off than participants in most other weight-loss programs and studies. In other words, the long-term weight reduction - in this case measured 6 years after the show - was successful.

The study found that while most subjects experienced substantial weight regain in the 6 years since the competition, the mean weight loss was 12kg and 57% of the participants maintained at least 10% weight loss. That's a good result compared to other weight-loss interventions that have been scientifically evaluated.

In comparison, one study found that in general, only about 20% of overweight individuals maintained at least 10% weight loss after 1 year of a weight loss program.

Only 37% of the lifestyle intervention arm of the US Diabetes Prevention Program maintained at least 7% weight loss after 3 years, and 27% of the intensive lifestyle intervention arm of the Look AHEAD trial (2014) maintained 10% weight loss after 8 years. 

Rate of weight loss does not predict the likelihood of regaining weight

None of those three studies cited above reported better success than The Biggest Loser! None.

In fact The Biggest loser was way ahead in both the average weight loss that was maintained per person and the percentage of participants who were successful.

Multiple studies, some of which set out to prove the opposite, have come to similar conclusions - that the RATE of weight loss does not predict the likelihood of regaining weight. 

What these studies have found is surprising. The most reliable predictor of long-term weight loss is how quickly you initially lose weight - and the amount of that weight loss. ​

Why does rapid weight loss prove to be the most sustainable?

The answer as to why rapid weight loss works best for long-term weight loss maintenance is not known.

The Biggest Loser Study set out to show that the metabolic rate of the contestants who maintained their weight loss had increased since the show ended. If this had been true it could have been argued that those who were successful were burning more energy than those who increased their weight.

The research results found that the opposite was true! Those maintaining their weight maintained a low metabolic rate. Hence, the actual metabolic adaptions resulting from rapid initial weight loss remain a mystery.

The X-factor - could it be exercise?

However there is a factor which The Biggest Loser Study does not mention - exercise. During the show the contestants undertake vigorous supervised exercise in conjunction with their diet.

Dieting and exercising concurrently builds the metabolic efficiency of the transportation of energy to our muscles, and the ability of our muscles to use that energy. Doing both together even improves the efficiency with which our fat responds to demands from our muscles for fatty acids.

Our muscles become more efficient at burning those fatty acids which are delivered from our fat stores via our blood, and our muscles learn to shift these fatty acids more deeply into their cellular structures. This makes the muscular energy stores more quickly available for contraction when needed.

These are some of the factors that lead to the Biggest Loser contestants burning incoming energy more efficiently and the maintenance of a lower metabolic rate. This is what happens with athletes.

How did those in The Biggest Loser Study who maintained their weight loss do it while maintaining the unexpectedly low metabolic rates?

I suspect that it was because those participants maintained an exercise regime post-show. As I mentioned above this was inexplicably not studied in The Biggest Loser Study.

However, this study of long-term weight loss using the US National  Weight Control Registry found that people who successfully maintained their weight loss had these common factors:

1. They engaged in high levels of physical activity ( approximately 1 hour/day),
2. Ate a low-calorie, low-fat diet,
3. Ate breakfast regularly.

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They also exhibited weight awareness - self-monitoring their weight - and maintained a consistent eating pattern across weekdays and weekends.

All good tips for us all to follow.

This study "Lessons from Obesity Management Programmes" cites ongoing regular physical activity as an important factor in maintaining long-term weight loss. 

Convincingly, this 2017 research of The Biggest Loser contestants found that those who kept their weight off had increased their physical activity by 5 times more than the "weight regainers". The study also found that there was little difference in the daily calorie intake of those who maintained their lost weight and those who regained.

Exercise was the key to keeping the weight off, not changes in calorie intake.

Consistent energetic exercise is required for long-term weight loss.

Three keys to success in maintaining long-term weight loss

Success Key #1 - Lose as much weight as healthy, safely and as quickly as possible

Research consistently shows that the most reliable predictor of maintenance of long term weight loss is how much and how quickly you lose it.

Rapid weight loss is something that you should seek advice about from your health advisor. It would typically require eating smaller quantities of high-quality, nutritious whole foods, unlimited vegetables, and avoiding flours, sugars, bad fats, and processed foods. And it may have fasting periods as well.

How rapidly, and how much you aim to lose, will depend on your individual circumstances.

Success Key #2 - Exercise more - at least moderately intensive exercise every day for one hour

Exercise improves the efficiency with which your body utilises your food. It also improves your muscle mass and your cardiovascular efficiency. All these add up to a lower metabolic rate and health benefits for your entire body including your brain health.

Ironically, a lower metabolic rate means that you will need fewer calories per day, or otherwise the extra will be deposited as fat. But because you are on a rapid weight loss diet your body won't be getting any "extra" calories. However your metabolism will still fight against you.

Your metabolism will read your rapid diet as potential starvation and go into "starvation protection mode". It will store as much energy as it can claw back from the usual energy needed to keep you functioning, and horde it rather than let you burn it. Exercise gets you access to those stores so that you can keep burning off your stored fat in defiance of starvation protection mode.

"Moderately intensive" exercise is not that which stresses your muscles and joints and requires taking rest days. Examples of exercises that you can do daily include brisk walking, using an elliptical trainer, swimming, slow bicycling, Zumba etc.

If you are already fit then you can step it up and do your intensive training 3 times a week, and moderately intensive on the other days as recovery.

It is crucial that you exercise during your weight loss as this is training your metabolism to be more efficient and to burn fat more efficiently over the long term. It is also critical that you keep up the exercise for as long as you want to maintain the weight loss.

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Success Key # 3 - Eat less after the diet - during maintenance - forever

Once you have finished your rapid weight loss, your metabolism will:

1. Be more efficient at using energy - the food you eat
2. Require less energy because you weigh less.

The combination of those two changes means that you need to reduce your on-going daily calorie intake in order to maintain the weight loss. The Biggest Loser Study found that participants required 600 calories less per day on average after the show than before their weight loss.

Six hundred calories are quite a lot. For example, if you were eating that amount daily — beyond your energy requirements — it would add about 2kg a month to your weight.

​And that's not the whole story. Before the losing weight the contestants the didn’t exercise. Now, the successful ones who are holding their weight gains are doing 5 times as much exercise as the regainers. 

That exercise takes energy; let's say 350 calories a day for moderately intensive exercise.

That means, in total, those holding their weight loss are consuming 950 calories a day less than before the contest. That's a lot. The reason that it is important to know this is that it sets your mental model of what life will be like after your rapid weight loss.

Your rapid diet experience will have educated you about good food choices. This feeds in to the good choices you need to make post-diet to reduce your calorie intake by about 1000 calories - plus add back in the calories for your exercise.

Check your new calorie requirements according to your new lower weight and your ongoing activity level, and adjust your food intake to match.

It's essential that you maintain a lower plateau of calorie intake, and preferably nutrient-dense foods.

Knowing your mets is how you will stick with your exercise program for longer

Here's how to get your mind set for long-term weight loss

Succeeding at long-term weight loss isn’t easy, but it is doable. If you approach your challenge with the right understanding of what needs to be done then you have a better chance of success.
Going into such a change with the right frame of mind will set your expectations up-front and help you maintain your motivation. There will be setbacks, but getting back on track is always only one meal and one brisk walk away.

The highest chance of success comes when you:

1. Undertake a fast-weight loss diet, with guidance from your health professionals
2. Start exercising during the diet, and maintain exercising afterwards
3. Reduce your post-diet food intake by about 950 calories - adjusted to a smaller reduction according to your level of exercise intensity.

The research shows that if you follow these three principles that you are most likely to maintain your initial weight loss over 6 years.​

Research has also shown that about 80% of overweight people are unsuccessful at long-term weight loss (when defined as losing at least 10% of initial body weight and maintaining the loss for at least 1 year). That 80% didn’t know what you know now — and that’s why you’ll be in the 20% that succeed.

Long-term weight loss is a real challenge but one which is achievable. Going in with the right mindset and expectations is step one. It is the first step towards an achievement that will last you the rest of your life and help you live longer better.

​Good luck.

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