When does the notorious yo-yo dynamic for weight loss and gain actually begin?

Yo-yoing is the maddening turnabout where you lose a chunk of weight … only for the weight to creep back on in short order.

A new study suggests the seeds of the yo-yo effect are planted when you first suffer obesity.

Researchers from ETH Zurich made this discovery when they went looking for the molecular causes of the yo-yo effect in mice.

To that end, they “analysed fat cells from overweight mice and those that had shed their excess weight through dieting”.

What they found was a little creepy: Fat cells stored ‘memories’ of obesity in their cell nucleus.

These memories remained “even after a weight-loss program, making it more likely for mice to put the weight back on”.

Translates to humans

The scientists discovered evidence that similar mechanisms are also present in humans.

Professor Ferdinand von Meyenn is head of the von Meyenn Nutrition and Metabolic Epigenetics Group and co-author of the new study.

He said: “The fat cells remember the overweight state and can return to this state more easily.”

He said the mice with these epigenetic markers regained weight more quickly when they again had access to a high-fat diet.

“That means we’ve found a molecular basis for the yo-yo effect.”

Epigenetic changes

You’ve probably heard of the genome, the entire set of DNA instructions we need to develop and function.

These are the sequence of building blocks that we inherit from our parents and they tend to be fixed.

The epigenome consists of chemical compounds that modify, or mark, the genome in a way that tells it what to do, where to do it, and when to do it. Different cells have different epigenetic marks.

Epigenetic markers, says von Meyenn, are more dynamic: Environmental factors, our eating habits and the condition of our body – such as obesity – can change them over the course of the lifetime.

But they can remain stable for many years, sometimes decades. During this time, they play a key role in determining which genes are active in our cells and which are not.

In the new research, obesity triggered epigenetic changes in the nucleus of fat cells – it was these changes that led to fat cells remembering and preferring the heavier state.

For fat cells, the shift in gene activity, prompted by weight gain, “seems to render them incapable of their normal function”, according to an article in Nature.

“This impairment, as well as the changes in gene activity, can linger long after weight has dropped to healthy levels.”

Consequences in people

Co-author Laura Hinte, a biologist at ETH Z, told Nature the results of the study suggest that people trying to slim down will often require long-term care to avoid weight regain.

“It means that you need more help, potentially,” she said.

But will these fat cells remember the obesity forever? Will time allow a person to start over, without the epigenetics cursing them. It’s yet to be investigated.

“Fat cells are long-lived cells. On average, they live for 10 years before our body replaces them with new cells,” Hinte said.

What about an intervention? It’s not yet possible to change the epigenetic marks and thus erase the epigenetic memory.

“Maybe that’s something we’ll be able to do in the future,” Hinte said.

“But for the time being, we have to live with this memory effect.”

Von Meyenn suggests: “It’s precisely because of this memory effect that it’s so important to avoid being overweight in the first place. Because that’s the simplest way to combat the yo-yo phenomenon.”