Why do the obese overeat ?

Another post inspired by a coincidence of two events - watching "65 Stone and Trapped In My House" and reading a couple of blogs after seeing Twitter references to them.

The TV programme was disturbing, to the extent where I nearly turned it off a couple of times. It centred on an obese man who had grown from 30 to 65 stone ( 910 lbs / 413 kg ) and become confined to one room in his own house and all but unable to move. Sadly the subject of the documentary died shortly after filming aged 33, from heart failure which was predicted by a bariatric surgeon who visited him for an assessment.

We saw the poor guy drinking full sugar pepsi while wallowing in his bed, and when his friends came round for dinner he wanted to eat the whole dish that they had made for sharing amongst five people.

Why does a man with at least 300 kg of fat stores feel the need to eat and drink 10,000 calories a day? When a dietitian suggested he would maintain at 7,000 and then should reduce by 1,000 per day in weekly steps he could not contemplate this and flat out refused - this was "too fast".

300 kg of fat stores is about 2.3 million calories so enough for 330 days energy supply at 7,000 a day. This is reminiscent of the infamous Scotsman "Mr AB" who did a water only fast for 342 days when faced with a similar dilemma - described here (including audio) and published by Stewart and Fleming. Unlike the unfortunate Carl Thompson (RIP) Mr AB lost 276 pounds, reaching his target weight of 180 pounds and maintaining the bulk of his weight loss. Over the five following years of observation, AB regained just sixteen pounds.

So what can we learn from a guy who on the night he died phoned a takeaway at 11pm to order apple crumble and two servings of ice cream, no doubt opening the conversation with his familiar "It's Carl and I'm starving". Was he suffering from persistent high levels of insulin, brought on by eating mountains of carbohydrate food, leading to much of his food intake being shuffled into fat stores leaving his metabolism still hungry ? This is the general statement of Gary Taubes' "Insulin Hypothesis" and further illustrated in Bob Briggs' Blog "Why are fat people hungry".

Bob quotes from the work of Dr Joseph Kraft who studies insulin levels and identified 4 patterns of insulin response to eating (the 5th pattern is minimal insulin response / Type 1 Diabetes) :

We know that fatter people generally have higher insulin levels and consequently release less fatty acids from storage into the bloodstream to use as metabolic fuel :

Also higher insulin levels reduce free fatty acid flux and concentration :

So the obese person with elevated insulin is denied access to the massive calorie reserves they are carrying and consequently live in a state of frequent hunger and consequent overeating with a proportion of what they eat being stored away as the carbohydrate portion further inhibits lipid oxidation.

The solution to unlocking the fat stores and reducing hungers lies in reducing insulin, through carbohydrate restriction and / or intermittent fasting. Even the Pattern 4 insulin response (green in the chart above) eventually falls after eating so a 16h fasting / 8h eating window approach may be beneficial.

The ketogenic diet, which is high in fat and low in carbohydrates, mimics the metabolic state of starvation, forcing the body to utilize fat as its primary source of energy. This also results in reduction in insulin levels. Once adapted to such a diet the consumers of an LCHF diet with moderate protein are, in general, not hungry, and frequently under-eat in clinical studies.

Evidence that carbohydrate restriction mimics total fasting has been provided by clinical studies where infusing lipids into the bloodstream at a rate equivalent to the Basal Metabolic Rate have little effect on outcomes - "carbohydrate restriction, not total energy restriction, is responsible for the increase in lipolytic sensitivity observed during fasting". S Klein and RR Wolfe have published several studies looking at lipolysis rates and the influence of various parameters on those rates.

From this and other reading I am drawn to conclude that :

1. Lack of fat release from storage leaves the fat person needing to eat for energy supply. Persistent hunger is a powerful motivator especially in the lonely or depressed.
2. Eating carbohydrates elevates insulin and reduces fat oxidation, reducing use of fats as well as their availability.
3. Elevated insulin responsible for locking up the fat also stores further dietary fat on the body. Eating carbs and fat together maximises this effect.
4. Carbohydrate restriction or fasting allows insulin levels to fall and unlock the fat reserves.
5. People on total fasts or 500-800 calorie modified fasts, or carbohydrate restriction to ketogenic levels, are not hungry and therefore do not typically overeat.