Although some diets are successful at reducing bodyweight in the short-term, it is very rare for a diet to maintain weight loss in the long-term.

In general, only lifestyle intervention strategies are properly able to produce sustainable results.

This is because weight loss and energy restriction results in a number of metabolic adaptations aimed at decreasing energy expenditure, improving metabolic efficiency, and increasing cues for energy intake [1].

There are also many physiological, neuronal and behavioral processes that seek to restore homeostasis, resulting in a strong drive for weight regain [2].

Because of these physiological adaptations to weight loss, the “reverse diet” concept has gained traction in hope to avoid the weight rebound effect that appears to be almost inevitable after any diet.

The latest analysis of the scientific literature concludes that ~35% of lost weight is regained 1 year following a diet, and 50% of people will return to their baseline weight within 5 years [3].

What Is A Reverse Diet?

A reverse diet is a term used to describe the period after a calorie-restricted diet, where people will try to avoid weight regain by slowly reintroducing calories back into the diet.

For this reason, “reverse dieting” has become incredibly popular among physique athletes.

However, to fully understand the principles behind the reverse diet, it is crucial to understand the fundamental concepts of energy metabolism and how they are affected during weight loss.

Understanding Energy Expenditure

Energy expenditure is the total amount of energy that is used by a person during a 24 hour period.

Total daily energy expenditure is comprised of 3 components:

• Resting metabolic rate – The minimum amount of energy spent to maintain bodily functions at rest.
• Physical activity – Energy spend during daily activities and exercise.
• Thermic effect of food – The energy required to absorb and digest the food we eat.

Establishing Your Resting Metabolic Rate

Your resting metabolic rate is defined as the energy needed to fuel minimal daily functions of cells and organs. In other words, it’s the amount of energy used to keep you alive when at complete rest.

On average, this accounts for ~60% of ones daily energy expenditure – depending on activity levels.

Weight loss is known to reduce ones resting metabolic rate, due in part to a decrease in metabolically active tissue (muscle), but also because of metabolic adaptations to energy restriction that prevent further weight loss. This improved energy efficiency is thought to be a survival mechanism when the body is in starvation in order to conserve energy.

These metabolic adaptations during calorie restriction are mainly thought to be an increased mitochondrial efficiency to produce energy, as well as a reduction in a concept known as “proton leak” [4].

Interestingly, this increase in metabolic efficiency and reduced resting metabolic rate is thought to persist for prolonged periods after weight loss phases have ended [5].

In turn, this reduction in resting metabolic rate increases the susceptibility of weight regain in the post-dieting phase, as energy expenditure is reduced whilst energy intake is increased [6] [7].

Unsurprisingly, a low resting metabolic rate is a clear predictor of weight gain over time [8].

Physical Activity

Physical activity is split into 2 components:

• Exercise-induced thermogenesis (sport, running, jogging, gym etc)
• Non-exercise induced thermogenesis (general daily activities and body movements)

Both of these types of activity are major individual contributors to increasing daily energy expenditure.

However, as weight loss progresses there is a measurable decrease in the energy expenditure from both types of these activities.

For example, energy expended during non-exercise induced activity, such as fidgeting, decreases when caloric intake is reduced because of subconscious psychological mechanisms [9].

It is your brains way of recognizing a reduction of energy coming in to the system, and compensating for it by reducing the amount of energy going out. After all, the body always attempts to maintain homeostasis.

Interestingly, there is also evidence to suggest that this spontaneous physical activity may remain suppressed for some time after people return to regular eating habits after a diet [10].

Again, this favors weight regain from a diet when caloric intake is increasing whilst daily caloric burn is still low.

The Thermic Effect Of Food

The thermic effect of food is the energy expended in the process of ingesting, absorbing, metabolizing, and storing nutrients from food.

On average, this accounts for ~10% of total daily energy expenditure.

This component of energy expenditure does not significantly change during weight loss, and therefore has little impact on weight regain after a diet has ended.

Do Hormones Play A Role In Weight Regain?

A number of hormones play key roles in the regulation of energy intake, energy expenditure, and therefore body composition.

In particular, the hormones of the thyroid gland, particularly triiodothyronine (T3), are known to play an important and direct role in regulating metabolic rate. Increases in circulating thyroid hormones are associated with an increase in the metabolic rate, whereas lowered thyroid levels result in decreased thermogenesis and overall metabolic rate [11].

Hormones secreted by fat cells themselves, called leptin and ghrelin, also have a large impact on modulating hunger levels and therefore can indirectly effect energy consumption.

Leptin functions as an indicator of energy availability, and during weight loss leptin levels are reduced which lowers the feeling of satiation from a meal [12]. Evidence suggests that the increase in stressors during weight loss, such as cortisol, may inhibit the action of leptin [13].

Conversely, the hormone ghrelin functions to stimulate appetite and food intake, and has been shown to increase during a diet when energy intake is reduced [14].

Further, there is evidence to suggest that unfavorable changes in circulating hormone levels persist as subjects attempt to maintain a reduced body weight, even after the cessation of weight loss protocols. This could increase the likelihood of weight regain.

So How Does A Reverse Diet Work?

A reverse diet slowly reintroduces calories into the diet in a strategic manner. This allows for gradual changes and improvements in the individual components of energy expenditure, and a stabilization of hormonal levels to avoid rapid weight regain [15].

This will subsequently reduce the differential gap in energy in versus energy out in the post-diet period, and therefore reduce weight gain.

In practice, a proper reverse diet will increase caloric intake by ~2-5% per week. This usually correlates to an additional 50-100 calories per week after a diet.

This is vastly different to the standard protocol of resuming prior dietary habits after a weight loss diet has ended, whilst metabolic functions are yet to fully recover. This is a key reason why fat cell hyperplasia is so common in the weight regain process [16] as part of a phenomenon known as “post-starvation obesity” [17].

While many of the metabolic adaptations to weight loss persist, a dramatic increase in energy intake should be avoided. Slow and steady wins the race.

This being said, despite making sense from a physiological standpoint, in addition to the vast amount of case reports from physique competitors, direct human studies are yet to fully analyze the reverse diet.

So far, reverse dieting has only gone as far as receiving positive mentions in sports journals based off the continually positive feedback in subjective reports.

More research is needed to verify the efficacy of periodic re-feeding and reverse dieting in supporting prolonged weight reduction and attenuating post-diet fat accretion.

Avoid Fast Weight Loss And Seek Lifestyle Changes

Although the reverse diet does help with restoring metabolic balance and avoiding post-dieting weight regain, it is only necessary after prolonged periods of significant caloric restriction.

In simple terms, the faster you lose weight, the greater the adaptations to weight loss will be (reduced energy expenditure) and the more important a reverse diet will become.

Fast weight loss is very common with the prevalent use of fad diets that are based around extremely low caloric intakes. This often results in producing only temporary success and leads to “yo-yo” dieting.

In an ideal scenario, the need for a reverse diet would not exist because people should be seeking lifestyle changes that revolve around less extreme dietary measures that are able to produce sustainable results.

Of note, a large study with over 100,000 people found that several habits could help gradually decrease and maintain weight over several years [18]:

• Eating healthy foods:Lean meats, fruit, vegetable, yoghurt, nuts, seeds and wholegrains.
• Avoiding junk foods:Sweets, chocolate, crisps, cakes.
• Limiting starchy foods:Eat rice, pasta and potatoes in moderation.
• Exercising:Aim to exercise for 30 minutes each day.
• Getting good sleep:At least 6-8 hours of sleep every night.

Conclusion

When a significant amount of weight is lost in short amounts of time, the body reduces its energy expenditure and manipulates hormone levels to favor weight regain.

Reverse dieting is a diet put in place after a weight loss phase to minimize body fat gain and restore normal metabolic and hormonal functioning.

It involves slowly reintroducing calories back into the diet to partially avoid the consequences of dramatically increasing calorie intake during a time in which the body is prone to storing fat.

We recommend anyone who has followed a calorie-restricted diet for some length to reverse diet once they have successfully reached a healthy bodyweight.