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Knowledge is power

Long-term maintenance of lost weight is one of the main challenges in treatment of obesity. Dr. David Macklin shares his perspectives on the driving forces behind weight regain and what can be done to address them.

7 key factors that influence weight regain

Long-term maintenance of lost weight is the primary challenge of managing obesity. In fact, 80% of lost weight is regained in the aftermath of a diet. 

So why is it so difficult to lose weight and keep it off?

Global obesity thought leader, Dr. Arya Sharma, Professor Emeritus of Medicine & Past-Chair in Obesity Research and Management at the University of Alberta, Edmonton and the founder and Past-Scientific Director of Obesity Canada (formerly Canadian Obesity Network), invited Dr. David Macklin, a member of the leadership team at the Medical Weight Management Centre of Canada (a virtual weight loss clinic led by medical experts), Director of Weight Management at the Mount Sinai Hospital BMI Clinic and Lecturer at the University of Toronto Faculty of Medicine, to share some thoughts on this topic.

Here, Dr. Macklin shares the 7 key factors contributing to weight regain and offers perspective on what realistic long-term weight management should look like.


“The principal reason for weight regain is biology. The brain defends against weight loss because of an old biological play book. If our ancestors lost weight, it was not to look good for a wedding or because of bathing suit season. Back then, weight loss was either because of illness or an interrupted food supply. Simply put, defending against weight loss was defending against death. 

In the last 30 years we have learned how the brain does this. The brain is expert at 1) recognizing fat loss, 2) defending against fat loss and 3) promoting weight regain. The brain does this by:

a) increasing appetite—the motivation for calorie intake

b) decreasing metabolic rate 

"Increased appetite seems to be more complicit than slower metabolism in weight regain. Increased appetite, in the form of an increased motivation to eat, leads to increased overall calorie intake, which in turn leads to weight regain.

"A reminder: the remaining reasons for weight regain operate through the main mechanism, biology.”


“The next common reason for weight regain relates to dieting. Note that dieting is not an effective method of preventing weight regain. Simply put, the risk of weight gain is greater the more 'diet-like' the weight-loss method. Specifically:

a) if the weight-loss effort involved a commitment to a reduced-calorie intake that was unsustainable

b) if the weight-loss effort involved a commitment to a level and type of effort that was unsustainable

c) if the weight-loss effort did not accept and involve a conscious commitment to the value of fun, food, drink, friends, socialization and travel

"The greatest predictor of thwarting weight regain is sustained adherence to the method used to lose weight. The above methods predict poor adherence. They also predict that for someone losing too much weight, going to a weight lower than what is sustainable, weight loss will be overwhelmed by biology.

"Thus, we have the definition of best weight. One’s best weight is arrived at by committing to the opposite of dieting. Best weight is discovered by committing to 1) a sustainable calorie level; 2) at a sustainable effort; 3) while accepting a conscious commitment to the value of fun, food, drink, friends, socialization and travel. Best weight is the weight you softly land at when committing to a lifestyle that is, by definition, sustainable.”


“The next and rather poorly understood reason for weight regain is a sustained change in one’s overall environment. A common current example of this would be someone who was working in an office and is now working in their home, or the opposite: someone who was working at home and now is working at an office. Another example is someone who, during weight loss, avoided high-risk settings for the purpose of weight loss and now inevitably is re-engaging in these setting. For example, someone who avoided social settings or restaurants temporarily just for the purpose of weight loss. The cues in our physical and social environments trigger the biological response of appetite—wanting—the subconscious motivation to eat. If the cues experienced during weight loss change, weight regain can follow.”


“If treatment is discontinued, the condition can come back. Evidence-based behavioural therapy has been demonstrated, if continued long term, to offer a defence against weight regain. Obesity medications (OMs) work by defending against an individual’s biology. OMs defend against increased appetite and dampen the subconscious motivation for calorie intake (wanting). If OMs are discontinued or poorly complied with, the defence against weight regain is lost and the biology does the rest.”


“A highly underestimated reason for weight regain is in an individual’s response to 'weight loss setbacks.' Common weight loss setbacks include 1) the aftermath of off-track eating and/or drinking episodes and 2) the moments after seeing a number on a scale not in one’s favour. Unless effective behavioural therapy has been provided, these setbacks may often be followed by negative self-critical thoughts and negative emotions including demotivation. Yet it is precisely when one is at a lower weight that they are most subject to their biological drivers of weight regain and most likely to experience over-consuming and unfavourable scale results. Screening for and treating these unhelpful cognitive responses is an important part of understanding and addressing weight regain. To reiterate, this is probably the most underestimated non-biological complication of weight loss.”


“Weight gain can be a possible serious side effect of many commonly used medications. Some medications more commonly cause weight gain than others, and significant inter-individual differences exist. Weight regain may be caused by the addition of a weight-promoting medication and if possible, a substitution can be made for an alternative medication that is more weight neutral.”


“Finally, there is a finite list of internal states that may promote weight regain. It is intuitive to most that stress, fatigue, lack of sleep, depressed mood and lower levels of activity may promote weight regain. For many individuals, especially in a state of reduced body weight, each of these factors can increase wanting, the motivation to eat, and decrease self-regulation skills (restraint). If someone is regaining weight, it is imperative to screen for each of these modulators and to recognize how a change in any of these may be leading to higher calorie intake and weight regain.”

Dr. Macklin further adds an important note regarding this list: “While biology is the most important and most common reason for weight regain, the other reasons can make the primary reason more complicated.”

Is obesity genetic?

Explore the research findings to this common question about the link between obesity and our genes. 

  1. Hall KD, Kahan S. Maintenance of Lost Weight and Long-Term Management of Obesity. Med Clin North Am. 2018;102(1):183-197.
  2. Wharton S, et al. Obesity in adults: a clinical practice guideline. CMAJ. 2020;192:E875-E891.
  3. Vallis TM, Macklin D, Russell-Mayhew S. Effective Psychological and Behavioural Interventions in Obesity Management. Accessed May 19, 2023. https://obesitycanada.ca/guidelines/behavioural
  4. Macklin D. Guest post: Reasons for Weight Regain. Accessed August 29, 2023. http://drsharma.ca/guest-post-reasons-for-weight-regain

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