Ask A Dietitian: Why do we gain weight back after a diet?

The expert said there's no foolproof way to lose weight, but there are common factors that make it difficult.

Welcome to Ask A Dietitian, a series where Yahoo Canada digs into food trends and popular nutrition questions with registered dietitian Abbey Sharp.

Abbey Sharp gives us the scoop on how to to lose weight long-term in the Ask A Dietitian series. (Canva)
Abbey Sharp gives us the scoop on how to to lose weight long-term in the Ask A Dietitian series. (Canva)

This article is for informational purposes only and is not a substitute for professional medical advice, diagnosis or treatment. Contact a qualified medical professional before engaging in any physical activity, or making any changes to your diet, medication or lifestyle.

Strict diets and trending hacks for dropping pounds have, in the past, taken over much of social media's wellness content. Though that's slowly changing, diet advice and before-and-after content continues to circulate.

But, what happens after the "after"?

According to registered dietitian Abbey Sharp, the weight likely comes back.

She tells Yahoo Canada there are ways to lose weight long-term, but there's no one-fits-all approach. Here's what you need to know.

Why do people try to lose weight?

Sharp warned weight loss and diets are a controversial topic, particularly the reasons why people choose to lose weight.

"People like to kind of exert their own beliefs onto whether or not a weight loss goal is valid, or is triggering or is problematic or not," the expert said.

'Diet culture' has kind of become a bit of a dirty word.Abbey Sharp

"As a dietitian, I always say I believe in body autonomy. And I don't believe it's really my place, as a practitioner, to tell somebody whether or not their reason for losing weight is valid."

Sharp explained if it helps a person improve their life in some way, that's valid reason enough to make some behavioural changes."

She added it's highly subjective and individual. Similarly, how someone loses weight is also individual.

How does losing weight even work?

A person's body needs a certain number of calories to maintain weight their individual homeostasis. (Getty)
A person's body needs a certain number of calories to maintain weight their individual homeostasis. (Getty)

Dietitian Sharp explained when we consume energy through calories, that energy gets stored in our fat cells as triglycerides. Our body needs a certain number of calories or energy to maintain weight homeostasis — this differs from person to person.

When we intake less calories or move more — also known as a calorie deficit —triglycerides get released from the fat cells and transported to the mitochondria. The fat cells are then broken down to make energy.

"That is the energy that we need to live and walk and do all the things that we do in the day. And if you maintain this calorie deficit, the fat stores basically continue to be used as energy, which results in a reduction in body fat," Sharp said.

Our body also releases carbon dioxide when the fat is broken down, which we essentially exhale out and our body releases water. That's why "a lot of initial weight is water and not just fat," Sharp explained.

However, what's important to know is that fat cells generally don't disappear when broken down — they shrink.

Those fat cells are still there... and can easily just expand again when you fall out of your calorie deficit.Abbey Sharp

"It's not like liposuction when we are removing some of these fat cells, they're still there and they've got that memory and can easily just expand again when you fall out of your calorie deficit."

That's not the only reason why it can be difficult to keep weight off.

Why does weight come back so easily?

There are many physiological and psychological factors that make weight loss difficult. (Getty)
There are many physiological and psychological factors that make weight loss difficult. (Getty)

According to Sharp, there are a lot of compensatory mechanisms that make significant and permanent weight loss a struggle for most people. However the three main physiological drivers are:

  • metabolism

  • activity levels

  • hunger

There are also psychological drivers.


Sharp explained when people diet and lose weight, their metabolism slows down by about five per cent, meaning they need about 50 to 150 calories less per day just to maintain the new weight.

That "can be very difficult for people who are already in a in a calorie deficit," she claimed.

Activity levels

When people diet, they subconsciously move less, Sharp said, which is also known as NEAT (non-exercise activity thermogenesis). It's not about working out, but the things we do subconsciously like fidgeting, tapping our feet, moving our arms and legs.

"Research in this area suggests that dieters, people who are in a calorie deficit, will burn 35 per cent, or about 350 calories less each day, just by subconsciously moving less."


During a diet, hunger hormones become elevated beyond baseline.

"If you've lost weight, or you're actively losing weight, your hunger hormones are going to go through the roof and your satiety hormones are going to go down. And of course, that is our body's desperate attempt to get us to back to where it wants to be — back to its state of homeostasis with our weight," Sharp explained.


Sharp said psychological drivers that make losing weight difficult are very common, particularly our reactions to deprivation of foods we like.

When we are deprived, our bodies don't like it and will fight to make you think and obsess about food.Abbey Sharp

"When we feel psychological deprivation, we're more likely to overeat the foods when we do get a rare chance," she claimed.

Because people don't like to be deprived, motivation to keep dieting tends to dwindle over time. "Food is one of life's greatest pleasures," Sharp added.

So, how can you lose weight and keep it off for good?

Pink measuring tape and fork on pink background. Slim concept. Healthy lifestyle.
When it comes to dropping pounds, slow and steady is best, the expert says. (Getty)

We've all heard the "fact" that 95 per cent of diets fail, but that's "a terrible statistic based on a really bad study," according to Sharp.

Sharp said there's no foolproof way to lose weight permanently and methods are highly individualized. For example, for a person who doesn't like carbs, a Keto diet might work great because they can keep it up without depriving themselves of what they want. For someone who likes carbs, a Mediterranean diet might work better.

"My take home message when it comes to diets... is: don't choose a diet because some celebrity or influencer told you. You should choose a diet that you feel absolutely confident that you can do for the rest of your life," Sharp claimed.

Slow and steady clearly wins the race.Abbey Sharp

Research showed the key to long-term weight loss wasn't going Keto or fasting, but rather the "basic" stuff, Sharp said, like:

  • Incorporating regular exercise into your workweek

  • Increasing your vegetable consumption

  • Ensuring that nutritious foods are easily available (veggies for snacks)

Sharp added, in her opinion, it's better to lose a smaller amount of weight and keep it off, than lose a huge amount and gain it all right back.

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