Elizabeth Berrett
If weight loss has ever felt like a condition for entry into your own happy life, Lisa Jansen knows the membership rules by heart—and she’s here to tear them up, politely but firmly. Her story doesn’t open with a miracle cleanse or a smug “before-and-after” flourish. It opens with a thought many people whisper to themselves in the dark, usually after a long day and a longer snack: “If only I could lose some weight, I would be so much happier.”
Jansen, author of One Size Does Not Fit All, once believed that line too—until life, as it tends to do, introduced nuance, mess, and the kind of self-awareness that doesn’t come with a barcode. Her central claim is disarmingly simple: the sustainable route isn’t happiness after the scale moves. It’s happiness first, and the scale can catch up when it’s ready.
A Life Lived in the “Before” Photo
Jansen describes a lifelong struggle with weight, not as a cosmetic inconvenience but as a defining reality. For much of her teens and young adult years, she says she would have been considered morbidly obese, “weighing in at over 135kgs at the heaviest.”
Like many people who’ve ever tried to out-sprint biology, habit, and emotion all at once, she did manage dramatic drops—twice. What followed was the more familiar part: regain, frustration, and the creeping belief that the problem wasn’t the plan, it was her.
“When I was 19, I managed to lose over 30kgs. But a couple of years later it was all back on, plus some more,” Lisa explains. “I was really frustrated with that and didn’t like myself much at the time. I wholeheartedly believed that I would be happy if only I could be skinny, but I just couldn’t figure out how to make that happen. Until years later in my late-20s when I figured out the real secret to long-term weight-loss.”
That last sentence is the hinge. Not a hack—an insight.
The Turn: Self-Discovery as the Missing Ingredient
In her mid-20s, Jansen began what she calls a “self-discovery journey,” sparked by a university professor and fuelled by reading on personal development, meaning, personality, self-awareness, and happiness. It’s the kind of list that can sound fluffy until you realise most people’s eating patterns have a biography.
“Learning about these topics opened my eyes to a whole new world. I learnt so much about myself, and it helped me gain clarity around who I wanted to be. These new insights gave me a new level of confidence. Around the same time, I got involved with a cause that gave me a real purpose and a sense of belonging. These two things combined resulted in me being much happier and liking myself more – and that gave me the strengths to tackle my weight one more time.”
Here’s the striking part: she doesn’t frame purpose and confidence as motivational posters. She frames them as leverage—psychological grip strength. Something you can actually hold onto when life starts throwing crisps at you from across the room.
The Result: 50kg Down, Nine Years Kept Off (Without Pretending It’s Easy)
Over the next two years, Jansen lost over 50kg and has kept it off for over nine years. She notes—accurately—that long-term maintenance is the real monster under the bed. (If you’ve ever “done well” for weeks then unravelled over one chaotic weekend, you already know.)
But she refuses the tidy ending. The honesty lands harder than the numbers.
“Food and weight management are still challenges for me. It doesn’t just go away. I still over-eat at times, and I still gain weight sometimes. The difference is that I feel in control now, and I always manage to get back on track before things get out of hand.”
That’s a maintenance mindset in plain clothes: not perfection, but recovery speed. Not never wobbling, but not letting a wobble become a season.
Why Diet Advice Often Fails in the Real World
Jansen’s argument is less “diet and exercise don’t matter” and more “they aren’t the whole story.” She points out a blunt truth: plenty of people already know the mechanics—eat better, move more, repeat. Knowledge isn’t the missing piece. Consistency is. And consistency is rarely a nutrition problem; it’s often an identity, stress, emotion, routine, environment, and belonging problem.
“When we talk about obesity and weight management, the conversation often tends to be focused on diet and exercise. But let’s be honest, most of us know exactly what we should and shouldn’t eat and how active we should be. We know what to do, it’s doing it, every day, over and over again that’s difficult.”
In other words: the battle isn’t the spreadsheet. It’s Tuesday afternoon.
Her Thesis, in One Sentence
Jansen flips the culturally popular storyline—lose weight, then earn happiness—and claims the sequence runs the other direction.
“Losing weight isn’t the key to happiness. Happiness is the key to losing weight. So when people ask me for diet and weight-loss tips, I always say to them: invest in yourself, get to know yourself better, find out what truly makes you happy and how being fit and healthy will help you achieve that – that’s what will give you the motivation to lose weight and keep it off.”
It’s a bold line because it challenges the marketable myth that the right meal plan will fix your inner weather. Jansen is basically saying: stop treating your body like the enemy and start treating your life like the project.
What the Book Actually Does (Not Just What It Claims)
One Size Does Not Fit All positions itself as a practical guide rather than a pep talk. Jansen’s framing is that long-term weight loss is “not about diet or exercise but about finding happiness,” and she builds the book around self-knowledge as the engine.
She argues individuality is the point, not a complication.
“I believe that when it comes to happiness, there is no one-size-fits-all solution. We are all unique. Different things will make us happy and different paths will get us there. One Size Does Not Fit All is about helping readers discover their personal path to a happier life.”
Structurally, the book is presented in three parts:
- Part one: exercises to explore personality, values, strengths, and weaknesses
- Part two: using that self-knowledge to identify what creates lasting happiness
- Part three: a “highly actionable” personal plan to build a happier life
Pros and Cons (Trust First, Hype Never)
Pros
- Maintenance-focused: It talks about keeping weight off—rare air in weight loss culture.
- Psychology-forward: Centres self-awareness, identity, and emotional patterns rather than pretending hunger is only physical.
- Practical structure: Exercises + plan-building suggests readers aren’t left floating in ideas.
- Honest tone: The inclusion of ongoing struggle is credibility you can feel.
Cons
- Not a quick fix: If you want macros, meal plans, or a strict training programme, this isn’t that lane.
- Self-work required: Reflection and exercises demand effort—some readers may find that confronting.
- May frustrate the “just tell me what to eat” crowd: The point is deeper than menus.
Who Is This Best For?
- People stuck in the loop of losing, regaining, and blaming themselves
- Readers who suspect stress, self-esteem, or emotional eating is driving the bus
- Anyone who wants a weight loss approach built around identity, purpose, and consistency—not punishment
- Those who like guided exercises and frameworks more than generic motivation
Is It Worth It? A Straight Value Read
At £9.99, the book sits in the “one takeaway could pay for itself” bracket—especially if it helps a reader shift from all-or-nothing thinking to a steadier, more forgiving system. The value hinges on whether you’re willing to do the internal work Jansen is asking for. If you are, the price is modest for a structured attempt at solving the part most diets ignore: the person doing the dieting.
Where to Buy
One Size Does Not Fit All is available to order for £9.99 at www.mortonsbooks.co.uk.
And if you’re still waiting for the day you feel worthy of a better life—Jansen’s point is simple: you don’t need to earn it with a smaller waistband. You build it first, and the body often follows.
