If you want to lose weight, dieting is not helping most people - fat, appetite and metabolism conspire to defeat our best laid plans, says a bariatric surgeon.

Dr Andrew Jenkinson has seen more than his share of patients who have failed on traditional diets, he told Jesse Mulligan in a radio interview.

He explains why we need to stop obsessing about calories and food fads in his book, Why We Eat Too Much: The New Science of Appetite.

'I've treated so many patients with very, very similar stories and they're all absolutely so desperate to lose weight that they have drastic surgery.”

These are people who have tried every diet under the sun and after initially losing weight, they regain it, sometimes plus some more, he says.

'When you look at the research, it's really well explained. We all have our own weight setting, which is basically a weight anchor, you can sort of drift up and down around this weight anchor for a little while, but you can't get too far away from it, it will actually pull you back towards your weight anchor.”

It's determined by genetics, the type of food you eat and if you try to diet away from the anchor, your metabolism will pull you back, he says.

'The metabolism is very, very dynamic, it can adapt to calorie restriction very powerfully.”

The basic message is; the body is better than will power in controlling your weight, the body is in control, he says.

Rather than trying to diet yourself away from that weight anchor, you have to address why that weight anchor is there, he says.

Lectin resistance

When you reach a certain threshold of obesity you get a condition called lectin resistance, he says.

'Lectin is a hormone that is released into your blood from your fat cells and it acts almost like a gas tank in your car, telling your brain how much energy is on board your body. The more fat you have, the higher the lectin level in your blood and the higher the lectin signal that acts on your brain, the weight control centre of your brain.”

If you over-eat for a period of time, like when you go on holiday, your lectin level goes up and when it's working a high lectin level will cause you to not want to eat too much and you'll drift back to the weight your body wants, he says.

'If you diet and your lectin level goes down because your fat mass has gone down, you will get voraciously hungry and your metabolism will go down.

'When you reach a certain threshold of obesity the information that's caused by the fat cells…plus the amount of insulin in your body, blocks that insulin signal to your brain.”

That's why you see people walking along the street who have got massive amounts of energy stored within their body, but the brain isn't getting that signal - the lectin level is very high but the brain is not getting that signal, he says.

Imagine you're driving along the motorway in your car and you see your gas tank meter shows you're about to run out of fuel soon you panic and pull into the nearest gas station to fill up, he says.

'But actually, when you fill up, you realise the tank is full already, it's the gas tank meter that's broken.”

It's a great analogy for people who are clearly storing too much energy, he says.

'Full blown obesity is a proper medical condition, and disease.”

Fats, oils and sugar

In the 1960s and 1970s, there was a scientific debate about what was causing a massive increase in cardiac disease particularly in men, says Jenkinson.

It was a fight between the sugar camp and the saturated fat camp, he says.

'It then came about that a lot of the money for the research for the anti-fat came from the sugar industry.”

It's why we now have it in our psyche that saturated fat causes heart disease, but the research shows us in actual fact, sugar is the big risk-factor, he says.

The evolution in obesity in Western populations came about when governments told us not to eat saturated fat and we replaced it with carbohydrate, he says.

'This has a really detrimental effect on increasing the average insulin levels of population and we know if you treat someone with insulin, their weight goes up. It's not a conscious decision.”

Andrew recommends reducing your average carbohydrate and sugar intakes to address your weight anchor which will improve your insulin levels "and seamlessly you will lose weight without going on a diet", he says.

De-stressing and reducing your cortisone level is also something you can do to bring weight down, more sleep and a more exercise can help with this, he says.

Polyunsaturated fats, vitamins omega 3 and 6 cannot be made in our bodies, he says.

In Western food, there is a massive predominance of omega 6, which creates a relative deficiency of omega 3 and the metabolic havoc that causes obesity, he says.

Omega 3 and omega 6 need to be in ratio, he says.

"They are competitive on every single cell wall of your body, and they are very important in signalling, particularly of insulin and it's the ratio of mega 6 and omega 3 that you take in your body ... you can take in a load of omega 3 capsules and tablets but actually if you're still frying up food with vegetable oils you're just washing away any good the mega 3 tablets are doing for you."

He recommends identifying the omega 6 sources in your diet and decreasing them.

The best fat to cook with is saturated fat such as butter, he says.

He is also an advocate of the 16-8 diet where you eat for 8 hours in a 24 hour period, he says this will mean your insulin levels improve significantly.

"And you will without any effort lose weight. I think the 16-8 diet is fantastic, just eat for an 8 hour window either have an early evening meal of skip breakfast."

RNZ.