I lost nearly 5st on weight-loss jabs. Ultra-processed foods have changed our brains… willpower isn’t enough any more: Ex-FDA head DR DAVID KESSLER reveals shocking truth

The first time I injected myself with one of the new GLP-1 weight-loss drugs in spring 2023, the effects kicked in within a few days. I lost my appetite. I felt bloated. Within 24 hours of injecting myself, I experienced intense chills and had to wrap myself in an electric blanket. I wasn’t ill – it was more like persistent discomfort.

Then my relationship to food began to change. Soon after I was having dinner with my family: ricotta-stuffed organic roasted chicken breast. Usually I would have dug in and likely gone for seconds. But that night I could hardly eat a bite.

It wasn’t just my appetite. My cravings also drastically changed. I no longer wanted salt, fat, sugar. I ate simple foods instead. Sometimes I would take only a little bread with butter.

I began eating vegetables on a regular basis for the first time in my life. I finally felt a freedom from a near-constant yearning, a break from ‘food noise’ – that clamorous chorus in our heads that plays on repeat throughout the day.

Seven months later I had lost 65lb (over 4st). My blood pressure had returned to normal and my blood glucose levels improved, taking me out of the pre-diabetic range. My body fat dropped from 33 per cent to 14 per cent. My waist had shrunk by 12in.

At that point, I decided to stop taking GLP-1 drugs, but not because of the side-effects I had experienced.

The reasons are deeper, more complex and more dangerous than that – but they concern pretty much everyone who is prescribed these medicines.

Throughout childhood, into midlife and still today I could gain 20lb to 40lb over a relatively short period, then painstakingly lose it – only to start the process all over again.

No one could accuse me of lacking discipline and determination. A paediatrician by training, I have headed two medical schools and I’ve led the US safety watchdog, the Food and Drug Administration (FDA, as commissioner under presidents George Bush and Bill Clinton). Obesity and weight management are part of my expertise.

Yet I have perpetually returned to this other realm, where I become an alternate version of myself. This person is impelled to eat without any sense of control, even as he knows it will leave him in a state of merciless self-consciousness and understands it is damaging his health.

Obesity is the root cause for major cardiovascular ills and metabolic diseases such as type 2 diabetes. It increases the risk of stroke and 13 types of cancer, contributing to nearly one in every five deaths in the UK.

I never plan to overeat. I’m driven to do so by the impulse that comes over me, and the illusory feeling that I’m going to satisfy myself once and for all.

For me, the cravings were always worse in the evenings. It was as if there were an alarm clock in my mind primed to go off a few hours after dinner, around 10pm. Once I finally relented, going to the kitchen for a snack, it was as if there were an electrode in my brain – urging me forward, insisting that I pursue pleasure – bite after bite.

I wanted to know more about what was going on in my brain when I had this 10pm craving rendering me powerless. So I decided to contact some of the leading addiction experts in the US.

The problem, as they explained to me, is that many people’s brains are susceptible to becoming addicted to irresistible, highly processed, highly palatable, energy-dense foods.

You might know these as ‘ultra-processed’ foods – I prefer to be more direct about what they are: I call them ‘ultraformulated’.

This focuses attention on the fact that much of what we are eating has been deliberately engineered to quietly commandeer the reward centres of our brains, delivering just the right combination of fat, salt and sugar (rarely found in natural foods) to trigger these circuits. But there is another component to these foods that has created a change in our brains and bodies. This is in fact the key energy supply for our brains and bodies – glucose (i.e., sugar).

Over millions of years, our bodies have developed and engaged mechanisms and hormones to handle glucose.

But over the last 100 years, all of that has changed. Our bodies are not designed to cope with the excessive loads of glucose (as well as fat) that we’re ingesting from ultraformulated foods – with the result being that we are flooding the addictive circuits in our brains. Food in its natural form – plant, meat or dairy – does not generally trigger our brains’ addictive circuits in a major way.

But ultraformulated food is really a very complex type of drug. And the more you eat ultraformulated food, the more quickly food cravings will reoccur – and with increased intensity. Early dependence sets in, resulting in compulsive use. And with that, the addiction cycle is well under way.

And yet for decades scientists have largely refrained from applying the term ‘addiction’ to ultraformulated foods for fear that it would sound inflammatory.

Some worry that labelling people living with obesity as ‘addicts’ would further the stigma attached to excess weight.

But given the manipulation of our food and the human biological susceptibility that makes us all vulnerable, food addiction is clearly not a reflection of personal failure, or a loss of willpower, but rather a human process.

Ultraformulated food is our new cigarette. It is critical that we understand the changes that need to occur – in our lives, in our bodies – through this lens.

In 1991, when I was the commissioner of the FDA, we took on the tobacco industry to halt what I considered to be a man-made epidemic. Big Tobacco had quietly and insidiously coaxed Americans into taking up a habit that is one of the leading causes of preventable disease and death.

We set out to examine the addictive qualities of nicotine and it became clear the meteoric rise in accessibility of cigarettes and a forceful marketing campaign – that is, a change in our environment – had caused a significant portion of the population to shift their perceptions and habits to accommodate a behaviour deeply corrosive to their health.

Similarly, the food industry has increasingly created an environment brimming with highly palatable, energy-dense foods – glutting our grocery stores, delis and corner shops with foods that deliver fat, salt and sugar that, when artificially combined, become irresistible.

Start feeding a laboratory animal such a diet for three weeks and a long-term memory for that preference stays with them. This is a big part of addiction.

Prolonged eating of ultraformulated food also robs us of the ability to feel full from traditional foods – essentially, it steals our satiety. This lack of satiety, as well as the reward system driving us to eat ultraformulated foods, makes obesity an incredibly complex disease to treat.

In early 2023, I left government service, two years to the day after I’d been asked to co-lead Operation Warp Speed for the Biden administration – responsible for all vaccines and drugs used in the Covid pandemic.

I’d been strapped to my desk for about 18 hours a day, seven days a week. It had been worth it. We’d defanged the virus. Yet personally all I could think about was that the circumference of my waist was as large as it had ever been. I’d gained 40lb (3st). So I began my familiar trudge.

In the past, I’d reliably been able to do this with a low-carb, high-protein diet as well as exercise. This time, however, after a few months of dieting, I’d only lost about 6lb.

I mentioned to my doctor that I was trying to lose weight but was frustrated. He told me that he was doing a clinical trial on some of the new weight-loss drugs that I, too, had been studying. Was I interested in trying one, he asked.

Under his direction, I injected myself then and there in his office.

I was as surprised as anyone about this. For most of my career, from my medical school days in the 1970s to my time at the FDA in the 1990s and beyond, I had doubted that there would ever be a highly effective drug for controlling weight.

But the GLP-1 drugs are able to target appetite. They work by slowing the time it takes for food to move out of the stomach – increasing nausea and dampening the brain’s reward response. In other words, they often make people feel too sick to eat.

When I started on them, I’d set a goal of reducing my weight to 175lb (12st), considerably lighter than my starting weight. But I reached that more quickly than I’d expected, so I shifted my goal to 155lb. When I reached that, I decided to adjust my target once again, this time to 137lb – which would give me a BMI of 20, well within the ‘normal’ range of 18.5 to 24.9.

With the help of GLP-1s, I reached a BMI I never thought I would achieve. More importantly – and what felt like a life transformation – my relationship with food had changed completely.

For a former sceptic like me, these drugs are an important development in taming obesity and navigating a healthier path through our modern landscape of ultraformulated foods.

The big question now is: how do we use them safely?

For while the drugs bring significant physical and mental health benefits for many of us, they are not for everyone – and they are not without substantial risks.

In part, this is because there’s no known method for stopping them without weight gain.

A year after stopping the medication, patients on semaglutide regain two-thirds of the weight they lost. If discontinuation rates remain this high, the drugs could turn out to be a real-world failure despite their impressive results in clinical trials. Their efficacy is also highly variable and individual.

People lose different amounts of weight, some don’t lose weight, some have even gained weight taking GLP-1s. These drugs also make food almost irrelevant for some people.

Dr Jens Holst, a professor of medical physiology at the University of Copenhagen, is concerned that nausea and other effects of taking GLP-1s will ultimately limit their long-term effectiveness. ‘Why do you lose weight?’ he asks. ‘It’s because you’ve lost your appetite and the joy of eating. The pleasure of a great meal is gone. How long can you endure that?’

That question will become increasingly relevant for next-generation drugs such as retatrutide. Judging from the early trials, it reduces appetite even more than the currently available GLP-1 drugs, semaglutide and tirzepatide. Professor Donna H Ryan, a leading clinical researcher in obesity, told me that with some of these newer drugs, people just stop eating and even drinking water.

They’re happy because they are losing weight, and don’t realise the danger they’re in. Dehydration is a real risk (in rare cases it may lead to kidney failure).

GLP-1s also raise the likelihood of pancreatitis – painful inflammation of the pancreas.

One of my major medical concerns about GLP-1s centres on delayed gastric emptying, which induces feelings of fullness.

But they may also create their own medical condition, delayed gastric emptying or gastroparesis. Patients need to take this seriously as it can lead to dehydration and malnutrition.

A study of people on GLP-1 drugs (published in Obesity in 2024) indicated that most patients experienced delayed gastric emptying during the first five weeks, with some maintaining that delay until the study concluded at week 16. Does gastroparesis persist after 16 weeks? We don’t know.

The prescribing information for the GLP-1 drugs currently omits any warning about gastroparesis. This must be corrected.

Up to 40 per cent of people taking GLP-1s may experience constipation. In rare cases, constipation can be deadly (causing intestinal obstruction, perforation and infection).

There is a rare metabolic condition associated with starvation, called euglycemic ketoacidosis, that we are beginning to see associated with people taking GLP-1s. Euglycemic ketoacidosis can lead to a significant drop in pH levels of the blood – the resulting condition, metabolic acidosis, can be life-threatening.

The fact that the anti-obesity medications are considered ‘forever drugs’, that people are meant to take for the rest of their lives, is particularly concerning given that we may not yet know all the longer-term adverse health consequences. And in fact, GLP-1 medications, powerful as they are, may not be sufficient for lifelong weight management.

Even if patients find the drugs effective, tolerable and affordable for years upon years (which is hardly a given), relying on pharmaceuticals alone to control weight does not address all the other aspects of human biology.

I was on a GLP-1 drug for seven months before I decided I didn’t want to stay on it indefinitely. I have now been off the drug for considerably longer than that.

I used GLP-1 drugs to reset my appetite. I do not view this as cheating or taking the easy way out. I improved my health, for now. What happens next month or next year is a whole other story.

My journey, like everyone’s, requires an ongoing effort. At one point, when my weight fluctuated up, I took up the injections again.

But at other times, I’ve preferred to stick with a healthy diet, rich in whole foods, and behavioural changes, such as strength training to preserve and build vital muscle. I’ve managed to keep my weight fairly stable ever since.

At one point I tried a continuous glucose monitor (like those worn by patients with diabetes) – it showed my blood sugar levels steeply rising and falling, driven by carbohydrates.

I found that going on to a low-carb diet flattened the fluctuations – and when I did this, I was less under the sway of food. My 10pm cravings didn’t entirely go away, but they did decrease.

I decided to test this new tolerance with what is, for me, the ultimate temptation.

One night, I walked into The Baked Bear in San Francisco’s North Beach neighbourhood, where customers create customised ice cream sandwiches – I’d made any number of my own creations here in the past, piling ice cream and candy between chocolate chips and M&Ms, then voraciously eating these concoctions on the spot.

But this time, I wasn’t tempted. I walked in and then back out again without ordering.

Using all the tools available to us, including GLP-1s, we can make improvements in our health that seemed out of reach even a few years ago. But nevertheless we are still just masking the source of the addiction.

If we truly want to make Western society healthy, we are going to have to take on ultraformulated foods. They are an assault on our health and, ultimately, our freedom and autonomy.

Many of the largest food companies seem to have forgotten that they are in the business of making food that their customers rely on to thrive.

Instead, this industry is slowly killing its customers. We desperately need a real food revolution.

Adapted from Diet, Drugs And Dopamine by David A. Kessler, MD (New River, £22), published 29th May. © David A. Kessler 2025.