Insulin makes you hungry (3) a matter of semantics and free fatty acids

OK. There is absolutely nothing technically incorrect with the description of the results contained within the title of this paper:

Effects of insulin-induced hypoglycaemia on energy intake and food choice at a subsequent test meal

They gave a small dose of insulin (low enough to not need rescue glucose within the study period) as a single bolus, waited for 20 minutes then offered the subjects an eat-as-much-as you-like buffet. This is what the glucose levels did

and this is the subsequent food intake in kcal:

That will be 1700kcal after an hypoglycaemic glucose of 2.0mmol/l or 1400kcal after a blood glucose of 4.5mmol/l. Glucose drop and kcal increase are both p less than 0.05.

Hypoglycaemia makes you hungry.

Next is this one, not quite so good because the title omits the word "insulin", but never mind.

Short-term nocturnal hypoglycaemia increases morning food intake in healthy humans

Here they infused insulin to a glucose nadir of 2.2mmol/l, stopped the insulin infusion and then infused glucose to normalise blood glucose concentration within 30 minutes. On one occasion the nadir was induced at the start of REM sleep (as early as possible in the night) and on another occasion it was induced about 3.5 hours later. Total sleep time was about six and a half hours on each occasion. At feeding time all of the subjects were normoglycaemic. The white column is the control, the hatched is from when the hypo was about six hours before feeding and black is from when the hypo was about three hours before feeding.

The conclusion is that an hypo soon before you eat makes you hungry (p less than 0.05). An hypo just after you have fallen asleep the evening before might do as well but the p value is ns for this test. In general we can say any hypo leaves you hungry.

But both studies did two separate things. They generated hypoglycaemia and they gave insulin. The assumption is that it was the hypoglycaemia which drove the hunger. Even if the hypoglycaemia was long gone at feeding time.....

Hallschmid (second paper) is a dynamo of publications showing central insulin (via the intranasal route) is an appetite suppressor. You've noticed that this second paper did not have a group given insulin combined with intravenous glucose to protect against hypoglycaemia, isolating the effect of the insulin alone. But then we all know what that would have shown.

Let's look at this from the real world point of view, which is: The function of insulin is the inhibition of lipolysis.

What happened to FFA levels in either study? We'll never know.

Many years ago I posted on a Spanish study cited by Dr Davis. It has all of the pictures you might need embedded in the post. From this we can say that spiking your insulin by eating a small (40 gram) high carbohydrate snack will produce a rise in insulin from 50picomol/l (normal fasting) to around 70picomol/l (a little bit higher but not much, full post-prandial insulin would be at least several hundred picomol/l) at one hour, with return to 50picomol/l by two hours. Despite this tiny rise in insulin the FFAs drop from over 400micromol/l to 100micromol/l at two hours (by which time insulin has actually normalised) with persistence of some degree of hypolipidaemia for up to another three more hours. This is a tiny increment of insulin compared to the above studies.

We know that hypoglycaemia without hyperinsulinaemia does not drive appetite. My hypothesis is that it's the insulin itself which drives a fall in FFAs, which in turn drives the hunger to rise, all secondary to insulin's anti-lipolytic effect. Note, there is no need for any direct appetite modulation from insulin to explain these results.

So: you eat a Mars Bar at 15.30, just before evening consults ('cos you had a long theatre list, you had no lunch and there was nothing else to eat. Looong time ago, but I can still remember those days). By 17.30 you are ravenous and a bit shaky. Ha! Reactive hypoglycaemia! Oh, but your BG is 4.5mmol/l. Huh?

Best measure FFAs.............

Peter

Insulin makes you hungry (2) even in the presence of hyperglycaemia

TLDR: The function of insulin is the inhibition of lipolysis. Really.

This is the paper cited by Woo:

Effect of Insulin and Glucose on Feeding Behaviour

The research group used real live humans. They looked several protocols but the ones we are interested in are those where they clamped insulin between 100 and 150microU/ml (high but plausible for post prandial on something like the SAD) and clamped glucose at either 150mg/dl (highish normal) or 300mg/dl (frank hyperglycaemia). They also had a control group (saline infusion) and an eu-insulinaemic with mild hypoglycaemia (50mg/dl) group. This is what the insulin/glucose values looked like, excluding the controls:

They asked the folks how hungry they were and got this sort of result:

I think the asterisks give the correct impression. However just for fun, at the end of the clamps, the subjects were allowed to suck a liquid meal via a straw through a barrier (so they couldn't see how much they were drinking). They ate/drank as much as they wished to. This is what happened:

The hypoglycaemic group was excluded from the eating trial because they had had all sorts of things done to get stable hypoglycaemia with eu-insulinaemia which involved somatostatin/replacement insulin and so precluded feeding in the immediate post-clamp period. We just have to accept the subjective appetite ratings for this group.

You would have thought that it would have been settled, back in 1985, that insulin in humans is an appetite stimulant. And that mild hypoglycaemia of 50mg/dl is not, provided there is no hyperinsulinaemia.

Of course this is a simplistic interpretation and quite possibly incorrect. Let's have a look at it from a more metabolic perspective.

What does insulin do?

The function of insulin is the inhibition of lipolysis.

So if we look at this current paper in the light of the 2011 paper we can make a more insightful interpretation of what is happening.

The people under hyperinsulinaemic clamps are not eating, because that is the study protocol. They are being infused with insulin at a time when they have no access either to any food or to their adipocyte lipid stores (and their hepatic glucose output will be near zero under the insulin clamp). Even the people under an hyperglycaemic hyperinsulinaemic clamp, who received around 700kcal of glucose over 150 minutes, are losing much of this glucose in to glycogen stores while simultaneously being deprived of adipocyte sourced FFAs.

The hunger may well come from metabolic energy deprivation rather than the insulin itself being an "hunger signal" of any sort. Insulin is the signal to store ingested calories. If it stores calories as if you have just had a meal when you haven't just had said meal, you are going to be hungry for those lost calories!

Peter

Insulin makes you hungry (1)

TLDR: The function of insulin is the inhibition of lipolysis. In the brain. In the periphery.

If you want to think about the central effects of insulin you could do a great deal worse than working through this paper:

Brain insulin controls adipose tissue lipolysis and lipogenesis

It is jammed full of exquisite quotes:

"To reduce the likelihood of pharmacological effects of the insulin doses administered, we choose a dose of insulin that is more than 15,000–fold lower than those commonly used for ICV [intra cerebro ventricular] insulin infusions (Air et al., 2002; Brief and Davis, 1984; Rahmouni et al., 2004)"

and

"An ICV (5 μl/h) or MBH [medial basal hypothalamus] (0.18 μl/h per side) infusion with either vehicle (artificial cerebrospinal fluid (aCSF) (Harvard Apparatus, Holliston, MA) or insulin (ICV 30μU; MBH 2 μU; Humulin R, Lilly) was started and maintained for 360 min"

and

"Both ICV and MBH insulin administration markedly suppressed the rate of appearance (Ra) of glycerol under basal and clamped conditions indicating that brain insulin, and more specifically MBH insulin signaling, suppresses lipolysis (Figs. 1B and C)"

and

"Hyperinsulinemia [systemic] induced by a 3 mU · kg−1 · min−1 clamp decreased the Ra glycerol by about 65% compared to a 1 mU · kg−1 · min−1 clamp in vehicle infused animals (Fig. 1C). Thus, at the doses administered, brain insulin infusion inhibited lipolysis to a similar extent as that achieved with peripheral hyperinsulinemia"


Here it is in pictures.

What does a CNS infusion of insulin do to lipolysis, at what are purported to be physiological dose rates? Obviously, it does exactly what peripheral insulin does, but using minuscule amounts; it suppresses lipolysis:

Of course, you have to ask how physiological is this "physiological" infusion rate? Insulin in the brain is thought to be derived from insulin secreted by the pancreas, so we are at liberty to ask what level of plasma insulin would produce a comparable level of suppression of lipolysis. The answer is an hyperinsulinaemic clamp of 3mU/kg/min, as in the above quote. That will be a clamp of somewhere around 70microU/ml clinically (3.5ng/ml in the paper), the sort of level of systemic insulin a healthy human might produce following a meal of real food, it's the column on the right of the graph:

Obviously the fall in lipolysis results in depressed FFA levels during the central insulin infusion, as you might expect:

The researchers didn't check the fall in FFAs from the peripheral 3mU/ml/kg clamp but I would expect it to be comparable to the central infusion level fall, glycerol appearance was equally suppressed by the central and peripheral administrations.

So one question (among many) is: Does this fall in plasma FFA levels result in hunger?

Oddly enough there are relatively few studies where humans have had experimental cannulae inserted in to either their cerebral ventricles or directly in to their ventomedial hypothalamus for insulin infusion. Ok, there are none.

But there are plenty of studies where humans have had systemic hyperinsulinaemic euglycaemic clamps performed. What is rare is to ask what the effect of such a clamp might be on hunger. Which brings us to another gem of a paper, this one from Woo. And it's good.

Peter

Butter gives you fatty liver! Again.

This paper is an absolute gem:

Saturated Fat Is More Metabolically Harmful for the Human Liver Than Unsaturated Fat or Simple Sugars

Obviously you have to be very careful in reading it. It contains no trace of understanding in its entirety, but the numbers in the results are fascinating.

How do we sum it up?

If you pay people to over eat 1000kcal per day for three weeks they gain weight and they gain liver fat. The group eating extra butter/coconut oil gain the most liver fat (IHTG is intra hepatic triglyceride). From Figure 1:

Unsaturated fat (22% omega six PUFA) causes less IHTG accumulation than saturated fat, similar to an excess 1000kcal of (mostly) sucrose. So saturated fat is bad for your liver and PUFA or sucrose are less problematic. Shrug.

Aside: Almost no-one gets fat because they deliberately over eat. People get fat accidentally, bit by bit plus the occasional splurge, which they cannot then lose. In this study people did NOT accidentally get fat against their will. They over-ate because they were paid to, whether they were hungry or not. Any resemblance to real life is purely accidental. End of ranty aside.

So anyway, let's get to the interesting bit. Lipolysis. The group measured the rate of glycerol appearance, a perfectly reasonable surrogate for the release of FFAs from adipocytes. Under fasting conditions I think you would agree that saturated fat group increased their rate of lipolysis, just a trend, ns, over the three weeks.

Here are the changes in the rates of glycerol release under an hyperinsulinaemic clamp:

OK. Under an insulin infusion of 0.4mIU/kg/min, plus a bit of glucose, the adipocytes which have been exposed to saturated fats are STILL releasing glycerol (and so FFAs). Eating a mix of olive oil, pesto and pecans for three weeks allows lipolysis to drop like a stone when you infuse insulin, p less than 0.01 between these two groups.

This is pure Protons in action. Saturated fat provides an high input of FADH2 at electron transporting flavoprotein dehydrogenase, so reduces the CoQ couple, so promotes reverse electron transport through complex I which will generate superoxide when the NADH:NAD+ ratio is high, ie under caloric surplus. Superoxide is the signal used for setting up insulin resistance, to stop caloric ingress. Beta oxidation of PUFA skips one FADH2 generation for each double bond present so they are crap at signalling insulin resistance by this mechanism. Even under caloric excess, insulin continues to act and packs more calories in to adipocyes. And it refuses to allow lipolysis. It even very slightly (and ns) reduces fasting lipolysis (in graph B above), when insulin is as low as it's going to get on the SAD (in Finland).

Now for some context.

What do we know about the adipocytes of the subjects at the start of the study?

The BMIs were 30, 31 and 33 in the three groups and of the 38 people involved in the study, 22 had impaired fasting glucose at admission.

So these people already have PUFA induced obesity plus complications. That means that their adipocytes have gravitated to a certain (large) size related to their absolute exposure to insulin combined with a PUFA enhanced insulin sensitivity. This adipocyte size is larger than it would have been had the adipocytes mounted the normal resistance to insulin's action which is provided by saturated fats. As caloric ingress made each adipocyte "full", this "fullness" should have be communicated from the mitochondria (as superoxide) to the adipocyte (as insulin resistance) and eventually the brain as satiety (that signal is VERY interesting, another day perhaps). Under PUFA any distended adipocyte does not feel "full", it behaves as if it is still hungry. Whole body hunger follows on from this. Thanks to the cardiological community and their love of PUFA.

Along come three weeks of palmitic acid (plus a few other nice saturated lipids). Now there is plenty of FADH2, a reduced CoQ couple etc etc and the adipocytes are suddenly able to resist insulin... They suddenly realise that they are grossly distended and there is now no way they are going to accept any more calories (even with insulin infused at 0.4mIU/kg/min). In fact, given this new-found "awareness" of their bloated size, they are going to off load as much lipid as possible, in resistance to insulin's bloating signal. This is why they release glycerol (and associated FFAs) in the face of an hyperinsulinaemic clamp...

Of course lipolysis is fine if you accept the fat from your adipocytes and stop feeling hungry, so stop eating. Developing adipocyte insulin resistance gets fat out of distended adipocytes, saturated fat delivers this.

Of course, if you are pouring FFAs out of your adipocytes but some clown is paying you to eat 1000kcal above your preferred daily intake, you are going to have to do something with those FFAs. Failing to take the chance of a hike to the top of some 1000kcal high hill, the fat will end up in your liver. The more lipolysis, the more fat in your liver. In real life you would simply eat less, we know that supplying small amounts of fat to the liver via the portal vein is a potent suppressor of appetite, at least in rats.

This why I love rodent studies of obesity. You cannot pay a mouse to overeat. Any obese mouse gets to be that way because it is hungry. If you make it hungry using linoleic acid to sequester dietary fat in to its adipocytes then its liver will be fine until adipocyte distension releases enough FFAs to then allow fatty liver to develop.

Sorry if all this sounds like a scratched vinyl record about Protons but people will take this current study as proof that saturated fat is bad for you, which is bollocks of course. Or simply as incomprehensible. One of my biggest problems is that the Protons concept provides a logical explanation for many of the "paradoxes" of different fat types. However it is something of a language of its own and I feel I have no shared vocabulary to explain what is going on with people who do not have the concept... Ah well.

Peter

BTW The sucrose arm is interesting too but that's another story for another day. You noticed the ns-reduced weight gain in the sucrose arm? I digress...

Oops

OMG, just seen how many comments are awaiting moderation now I'm back to occasional posting. Groan. I'll see what I can do, if desperate I'll just delete the spam and hit post for them all. Apologies for the inattention over the past few weeks.....

Peter

Acipimox and insulin

Woo had a bit of a rant about acipimox. Here's my simplified idea.

I've been interested in acipimox, in a round about sort of a way, for a very long time. To me, the core fascination is that it is not only an effective suppressor of lipolysis, but it is pretty well weight-neutral and it most certainly does not result in weight gain.

Which, you have to admit, is interesting.

How can this be? I feel something of a clue can be found in the studies using a similar drug, nicotinic acid. Both drugs effectively suppress plasma free fatty acids via the same receptor but the neatest study happens use nicotinic acid.

People may recall that I posted about the role of FFAs in the secretion of insulin as demonstrated by an isolated rodent pancreatic preparation, some time ago. The core concept here is that insulin secretion is dependent on the chain length and saturation of the FFAs used for perfusing the pancreas along with the glucose. This phenomenon appears to be well appreciated by the authors of this next paper (same research group):

Circulating fatty acids are essential for efficient glucose-stimulated insulin secretion after prolonged fasting in humans

So what happens to in-tact humans when you fast them for 24 hours (to raise FFAs) and then bolus them with intravenous glucose? Or fast them, artificially drop their FFAs with nicotinic acid, and then bolus them with glucose? This is what happens:

I think it is reasonable to state that dropping FFAs acutely, using nicotinic acid, results in a 50% drop in the area under the curve for insulin secretion over 60 minutes for a given bolus of glucose. The more speculative idea is that dropping insulin might reduce lipid uptake in to adipocytes. I don't know. It's an interesting idea.

If we simply consider acipimox to be a long acting analogue of nicotinic acid we have here a potential explanation for why it fails to induce weight gain. It might just simultaneously lower insulin levels. Understanding acipimox appears to require some insight in to the insulin hypothesis of obesity, not a notable feature in certain areas of obesity research.

Failure to appreciate the roll of insulin in obesity will limit any sort of understanding of the condition or the drugs which might or might not influence it. Seems that way to me.

Peter