Extreme dieting can be counterproductive and even dangerous. We spoke to bariatric surgeon and author of Why We Eat (Too Much), Dr Andrew Jenkinson, and registered nutritional therapy practitioner, Julia Young, about the consequences of rapid weight loss.

The following is extracted from a feature by Hatty Willmoth, in the Summer 2022 issue of Optimum Nutrition.

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Crash diets involve drastically reducing daily calorie intake to try and lose weight fast.

Think Kim Kardashian trying to fit into the vintage Marilyn Monroe dress at the Met Gala, or a young woman preparing for ‘hot girl summer’, or a bride trying to fit into a too-small wedding dress.

And crash dieting may be on the rise, thanks to pandemic-related weight-gain.

Private healthcare provider Bupa observed a tremendous rise in internet searches related to crash dieting between January and December 2021.

Searches for ‘easy ways to get skinny’ doubled; searches for ‘extreme weight-loss methods’ grew by 387%; and searches for ‘detox drinks to lose belly fat’ soared by 800%.

But for some people, crash dieting is a regular feature of the summer months. This is called yo-yo dieting; losing and gaining weight cyclically.

Regardless of the specifics, crash dieting is not a good idea.

Quick weight loss: the immediate risks

We spoke to registered nutritional therapy practitioner Julia Young about the risks associated with rapid weight loss.

Here are some of them:

• Dehydration, after losing a lot of water
• Losing muscle tissue, including from vital organs
• Rapid release of toxins from fat cells
• Deficiencies in vitamins and/or minerals (which can lead to frequent illness, thinning hair, low mood, irritability and dizziness)
• Persistent tiredness and fatigue
• Low blood sugar and blood pressure (which can lead to light-headedness, nausea, blurred vision, confusion and fainting)

Extreme patterns of eating can even be precursors to full-blown eating disorders.

In the long term, the strain of drastic weight loss can increase the risk of brain damage, diabetes, altered immune function, liver and/or kidney failure, heart attack and stroke.

How to maintain weight loss

Rapid weight loss is rarely sustainable.

Young says: “You quite often see people promoting losing a stone in a couple of weeks or something, and it’s very attractive.

“But more often than not, people regain the weight because if you return to the way you’re eating, you’re going to put that weight back on.”

Even on moderate diets, weight loss is difficult to maintain, yet Andrew Jenkinson, a bariatric surgeon and author of Why We Eat (Too Much), says there is some evidence to suggest that “the faster you lose weight, the faster you regain it”.

Metabolism and weight loss

This is largely due to hormonal changes.

Weight is determined by the hypothalamus, the part of the brain that keeps us in a state of homoeostasis (stability), and which maintains our ‘weight set point’ — the ‘ideal weight’ determined by the brain.

It does this by releasing different amounts of hunger and satiety (fullness) hormones, and by altering our basal metabolic rate (BMR).

This is the amount of energy it takes to run a human — to beat a heart, inflate and contract a couple of lungs, maintain a constant internal temperature, and so on — and makes up about 70% of the energy we normally use.

The hypothalamus adjusts our BMR in response to available and needed energy, so when we eat less, we burn less energy.

In other words, when we lose weight, our metabolism becomes more efficient.

Why am I so hungry?

Hormones powerfully control how hungry a person feels. Ghrelin, secreted by the stomach and known as the ‘hunger hormone’, could bend even the strongest of wills.

Jenkinson explains what happens during a crash diet: “That ghrelin level will go very, very high and you’ll have this voracious hunger and food-seeking behaviour.

“Hormones guide your body, tell it what to do. It’s very hard to resist those instructions.

“So, when ghrelin is sky high, it is almost impossible to walk past a Starbucks. It’s like a man walking past an oasis in the desert when he hasn’t drunk water for three days.”

Furthermore, he explains, fullness or ‘satiety’ hormones should trigger us to stop eating once we’ve started, but on a crash diet they go “very, very low, so when you do start eating you can eat a lot before you stop”.

Long-term effects of weight loss

Crash dieting can permanently impact a person’s weight.

The body doesn’t recognise a deliberate diet; it reacts as if it’s living through a famine.

And, when that famine is over, it wants to be prepared for future famines by keeping more fat in its stores.

Therefore, after a crash diet, your weight set point (the ideal weight your body aims to maintain) shifts upwards.

You’ll likely end up bigger in the long run than you were before.

How to lose weight: a health-first approach

Instead of crash dieting, Young advises that those who want to lose weight aim to improve their health.

“Rather than saying, ‘I want to drop a dress size by this certain date’, focus on your health and how you feel. By doing that, the weight should naturally come off. Rather than counting calories, count nutrients.”

Weight loss tips

Young recommends addressing several areas to lose weight sustainably.

• Portion sizes: “using your hand as a guide, protein should be the size of the palm of your hand, the cup of your hand is what you want for carbohydrates, and then [the tip of] your thumb for your healthy fats — oils, butter, and things like that — and a good handful for the veg.”
• Snacking: focus on three meals a day, with four- to five-hour gaps between eating.
• Sleep: “Poor sleep impacts the hunger hormones — even one night. The next day we crave sugar, carbohydrates and just don’t eat as well.”
• Stress: “Cortisol, the stress hormone, is a fat-storing hormone, so if we’re constantly stressed, that’s going to encourage us to store fat.”
• Underlying issues: if you’re struggling to lose weight, talk to your doctor – particularly about your thyroid

Building habits for life

Young says that those considering a quick-fix diet should think deeply about what they actually want.

“Do they want to lose this weight for a beach holiday and then they’re happy for it to go back on, which we know is not healthy anyway?” she says.

“Or do they want to make sustainable changes that they can use for the rest of their life?

“We don’t think about brushing our teeth twice a day, it’s just a habit, and that’s what you need to get to when making small changes; so you don’t need to think about the fact that you’re eating this healthier meal or you’re not snacking anymore. It just becomes a habit.”

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