Overfeeding humans: Jebb

"Obesity implies a failure of autoregulatory homeostatic responses to caloric excess"

The quote comes from this paper first authored by Mario Siervo but with Susan Jebb as the group leader. I'll discuss the paper in a moment.

Who is Susan Jebb?

From the Medical Research Council website:

Cross-government 2007- Chair, Expert Advisory Group on Obesity - Susan Jebb

Department of Health 2006 - Chair, Expert Group developing the Healthy Living Social Marketing Programme - Susan Jebb

Department of Health/Food Standards Agency 2004-2005 Expert Working Group on Nutrient Profiling - Susan Jebb

Government Office for Science 2006-2007 Science Advisor, Foresight Project 'Tackling Obesities: Future Choices' - Susan Jebb

You get the idea. An obesity politico. This sort of politico. Also check the date on that link. 2003. I was just starting on low carbohydrate eating at the time. Jebb was all over the papers. One very obvious thing, to someone who had just read Atkins' "New Diet Revolution" from cover to cover, was that none of the experts being quoted had read the book!

So that puts Jebb in context. Here's the interesting study on overfeeding humans rather than dogs. This is the feeding protocol:

3 weeks run in feeding
3 weeks 20% extra calories
1 week rest, eat as much of a Jebb diet as you feel like
3 weeks 40% extra calories
1 week rest
3 weeks 60% extra calories
3 weeks rest

This is the table detailing exactly what was eaten.

These are the weight changes, also subdivided in to tissue composition.


This is the executive summary: People got fat on the excess calories and couldn't loose the weight within 3 weeks. Some people couldn't loose any of the weight at all.

Jebb's conclusion. People pig out at Christmas and fail in their New Year diets. Greed and sloth, greed and sloth. Once you've pigged out, if you're greedy, you'll keep troughing.


Now, let's ignore Jebb and look what happened.

Protein was increased from 85g/d through 101g/d, 112g/d to 126g/d from baseline through over feeding protocol. Some increase, but not unreasonable.

Fat was used to increase the "energy density" of the diet and so was increased from 120g/d through 158g/d, 196g/d to 231g/d. The later being Kwasniewski levels for optimal health (but without the carbs!).

Carbs started at 322g/d and ramped up through 375g/d, 409g/d to 446g/d. Okayyyyy. Interestingly, just reducing these carbs to a tenth of this overfeeding level would have given quite easy weight loss for most people, with the fat left alone!

There were snacks too but they don't affect the basic argument.

Jebb is a calories in calories out sort of a person, so fructose is the same as glucose to her. We'll never know how much fructose was fed.

Now let's look at substrate oxidation. With all that increased fat intake what happened to fat oxidation? (All of the values are approx and from the figure)


With a fat intake of 4.5MJ/d fat oxidation was 4.5MJ/d. Neat that!

On 20% overfeeding fat intake went up to 6MJ/d and fat oxidation DROPPED to 3.8MJ/d.

On 40% overfeeding fat intake increased to about 7.7MJ/d and oxidation DROPPED FURTHER to 3.5MJ/d.

On 60% overfeeding fat intake was 8.5MJ/d and fat oxidation seems to have bottomed out at 3.5MJ/d, no further drop.

Three points,

Carbohydrate oxidation went up as carbohydrate intake increased. This cannot happen without insulin. Increased carbohydrate oxidation means increased insulin, certainly at this level of increase of glucose oxidation. Jebb either doesn't know this, and is an idiot, or does know this and didn't measure insulin for a personal agenda. I favour the idiot theory with Jebb. I guess you could argue insulin sensitivity increased but this is a study of gross overfeeding, so that's unlikely.

Fat oxidation decreased with increased calories. What controls lipolysis? Insulin. More insulin, less lipolysis. Less lipolysis means less fat oxidation. Fat is stored more effectively and is locked in to storage. You can't oxidise stored fat.

Body water went up. Water retention means sodium retention (water retention without sodium retention = hyponatraemia = death). Sodium retention is a hallmark of elevated insulin acting on the kidneys.

In a short communication the same group measured leptin and ghrelin levels, which indictaed everything should be hunky dory for return to normal body weight, but clearly things weren't. That's assuming leptin satiates and ghrelin makes you hungry. In a simple balance of energy in vs energy out, weight is controlled by appetite. This being a Jebbish paper, they didn't measure insulin. They didn't measure the primary fat storage hormone. Oh, Susan, how could you not do this?

So what really happened in this study?

Weight gain, to anyone with half a brain, is a phenomenon of the diversion of ingested calories to storage as adipose tissue. Metabolic fuel requirement must be met at the cellular level, above that calories can go to storage as fat. Weight loss means the body gaining access to stored fat calories. Hunger controls eating behaviour when there is no artificial requirement to over eat by 60%. Hunger will adjust food intake until there is an adequate supply of metabolic fuel for the whole body.

If a large chunk of those calories consumed go in to storage, even without overeating, you will maintain hunger until you achieve enough AVAILABLE calories which are needed to run your metabolism. Whether these come from food or bodyfat depend on blood insulin level. High insulin levels lock energy in to fat, so you must eat more food to obtain metabolic fuel. Hence you don't lose weight because energy locked in to bodyfat isn't being used.

You don't need to measure insulin to know it goes through the roof when you eat nearly half a kilo of carbohydrate in a day. You don't need to measure insulin to know it is elevated when you see fatty acid oxidation plummet. You don't need to measure insulin to know it is elevated when you see glucose oxidation rise.

You MUST measure insulin if you want the readers of your scientific publications to think you remotely know anything about weight control and are in a position to advise the nation.

Ultimately, the verdict on Susan A Jebb will be that she she did not measure insulin.

Peter

Oh, and weight loss was impossible for some people, they were the ones who got most fatty liver infiltration per unit fructose ingestion. As a guess.

Thanks to Robert for the link to the papers in this post.