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Saturday, October 5, 2013

Glucagon, Dietary Protein, and Low-Carbohydrate Diets



Glucagon is a hormone that plays an crucial position in blood glucose management.  Like insulin, it truly is secreted by the pancreas, however it truly is secreted by a various mobile inhabitants than insulin (alpha vs. beta cells).  In some techniques, glucagon opposes insulin.  However, the part of glucagon in metabolic rate is regularly misunderstood in diet program-well being circles.

The liver generally stores glucose in the form of glycogen and releases it into the bloodstream as required.  It can also manufacture glucose from glycerol, lactate, and particular amino acids.  Glucagon's principal task is to hold blood glucose from dipping too lower by creating confident the liver releases ample glucose.  There are a couple of scenarios where this is especially critical:

  1. Hypoglycemia.  When blood sugar drops below a specified threshold, for instance if a diabetic injects way too considerably insulin, the brain senses it and initiates a response (the counterregulatory response) to carry glucose back again up and prevent unconsciousness and death.  Glucagon launch is an important element of this response.

  2. Fasting.  Glucagon assists assist blood glucose stages during fasting, when glucose ingestion is zero, by stimulating the manufacturing and launch of glucose by the liver.  This sustains the brain, which has an absolute prerequisite for glucose (however it can derive some power from ketones).

  3. High-protein foods.  Protein stimulates insulin release as much as carbohydrate does (due to the fact a single of insulin's jobs is to ship amino acids into lean tissues this sort of as muscle mass), but protein doesn't source fast glucose like carbohydrate does.  If this process went unchecked, consuming a substantial-protein food would cause hypoglycemia because insulin launch would suppress blood glucose as well considerably.  Glucagon release counterbalances insulin, preventing hypoglycemia when we take in a higher-protein food.


This publish will talk about the third situation.  If we are searching to reduce circulating insulin ranges employing diet plan, which is ostensibly the objective of specified low-carbohydrate diet regime methods, lowering carbohydrate ingestion is only half the tale.  If we genuinely want to eat reduced-insulin foodstuff, the initial point to do is search up which foods in fact elevate insulin pursuing a meal.  The knowledge, released in a paper titled "An Insulin Index of Meals", may shock you.  This paper is totally free entry.

What we see right absent is that higher-protein foodstuff usually encourage insulin to a comparable, at times even increased, diploma than substantial-carbohydrate foods, calorie for calorie.  Beef and fish launch as much insulin as brown rice.  Pasta (white or brown) and porridge launch less insulin per calorie than cheese, beef and fish.  Donuts are only 25 % increased than fish.  According to the paper, the five lowest-insulin meals analyzed were (from most affordable to highest) peanuts, eggs, bran cereal, white or brown pasta, and grain porridge.  Doesn't audio very low carb, does it?

People often cite glucagon to solve this difficulty.  The concept goes like this: glucagon is the opposite of insulin, and if they are launched with each other, as they are when you consume a high-protein food, then their consequences on blood sugar, on hunger, and on excess fat metabolic process cancel one particular yet another out in a way that they would not adhering to a carbohydrate-heavy food.  If we are speaking about blood glucose, this is correct.  Glucagon does much more or much less terminate out insulin's influence on blood glucose, and ingesting protein in isolation does not direct to major alterations in blood glucose.

Concerning starvation, glucagon is often proposed to oppose the hunger-inducing outcomes of insulin.  However, opposite to well-known claims, insulin does not improve hunger or foods intake in human beings until it causes frank hypoglycemia, so there is nothing to oppose (one, 2, three, four)*.  Nevertheless, glucagon probably does perform a function in satiety, independently of insulin.  So that declare is partially accurate.

If we contemplate the claim that glucagon promotes unwanted fat launch from excess fat tissue, out of the blue we're on shaky ground!  When researchers place high doses of glucagon on unwanted fat cells in a petri dish, or give very large doses of glucagon to animals or humans, it stimulates the release of fat (lipolysis).  So the thought that glucagon counterbalances insulin's outcomes on lipolysis does have some basis in fact.  But supplying individuals reasonable doses of glucagon, doses that approximate what would happen by natural means in the human body subsequent a high-protein meal, does not enhance lipolysis (five, six).  Also, blocking glucagon motion in dogs does not minimize lipolysis, suggesting that baseline glucagon amounts are unrelated to lipolysis (7).  The glucagon receptor knockout mouse is in fact lean and resistant to diet-induced obesity, opposite to what these claims would forecast (8, 9)**.  That's why contemporary evaluations, these kinds of as Keith Frayn's textbook Metabolic Regulation, make statements this sort of as these:


Glucagon has a powerful influence in isolated unwanted fat cells in the laboratory, but appears not to impact excess fat mobilization in human beings in vivo.



Glucagon almost certainly does play a position in satiety (fullness).  As with numerous other satiety peptides introduced by the digestive tract and pancreas, glucagon is sensed by nerve terminals that ship impulses up the vagus nerve, and the signal is transmitted to the brain where satiety is perceived (10).  In the case of glucagon, the related receptors are positioned in the liver, exactly where glucagon mediates the greater part of its effects***.  Injecting glucagon decreases foodstuff ingestion, and blocking glucagon action increases meals ingestion, however the evidence has not constantly been consistent (eleven).  Protein, and to a lesser extent liquor and excess fat, but not carbohydrate, direct to improved glucagon secretion subsequent a food (twelve, 13, fourteen).  Increased glucagon secretion could be 1 cause why large-protein eating plans direct to decreased foods intake and physique fatness in over weight folks, even though other convincing mechanisms have been proposed****.  The body's response to food is so complicated that it truly is challenging to predict huge-scale (and lengthy-time period) physiological alterations by measuring a one hormone, but it seems most likely that glucagon plays a function.

Whatever the system, protein remains the most satiating macronutrient, and it does assist with body fat decline.  In reality, modern proof suggests that the ability of low-carbohydrate eating plans to promote fat decline and routine maintenance (relative to lower-fat diet plans) might have far more to do with improved protein than reduced carbohydrate (fifteen), at least at a average level of carbohydrate restriction.  It is known that high-protein, high-carbohydrate, minimal-fat diet programs are successful for excess fat decline, and this diet plan stimulates a huge quantity of insulin launch (16, seventeen).

In one particular especially interesting study, rising protein consumption at the price of unwanted fat (with no adjust in carbohydrate percentage) led to a spontaneously decreased calorie intake and substantial unwanted fat reduction that was comparable or excellent to what is usually noticed in minimal-carbohydrate diet plan research (18), notably taking into consideration that the participants ended up only modestly overweight at baseline and have been not even making an attempt to drop bodyweight.  Both fasting and post-food insulin stages remained unchanged throughout the intervention.  None of these results seem to involve the meant influence of glucagon on unwanted fat cells, or anything at all associated to insulin, though they could relate to the outcomes of glucagon on satiety.

With each other, this paints a complicated photograph, suggesting that the efficiency of lower-carbohydrate diet plans for fat loss in chubby people:

  1. Relies upon at the very least in component on improved protein consumption.

  2. Most likely does not need a reduction of insulin secretion, but may involve an enhance of glucagon.

  3. Almost certainly does not require direct outcomes of glucagon on body fat cells, but could relate to glucagon's consequences on satiety, and probably other effects in the brain.


Over and above the metabolic/hormonal outcomes of reduced-carbohydrate or high-protein diets, these diets may also be powerful because of changes in the reward and palatability price of the diet (and foodstuff variety, a connected issue).  Getting rid of pastries, donuts, soda, fries, and pizza goes a extended way, and taking one particular or far more objects off the desk (e.g. bread) tends to minimize total meals consumption even if every little thing else continues to be the same.  The potato-only diet regime is a great example of this (19, 20).  Over on Mark Sisson's discussion board, a quantity of individuals have been repeating Chris Voigt's experiment of consuming nothing at all but potatoes, with similar excess weight loss outcomes (21).  To be clear, I am not recommending this strategy, but it certainly illustrates the power of a monotonous diet.  Interestingly, apart from currently being very filling for every calorie, potatoes are also a single of the most insulin-stimulating food items, according to the paper cited above.

* I am informed of a single older research where rising insulin did direct to starvation and increased foodstuff ingestion independently of hypoglycemia.  That paper experienced the minimum convincing review design and style, but I included it for completeness.  It's the previous of the four references I provided.

** They also have much higher ranges of GLP-1, which may possibly be a compensatory adaptation, and most likely plays a function in the general phenotype.  GLP-1 is an incretin hormone as well as a satiety hormone.  Incretins are a team of peptides that encourage insulin secretion.  This is the dilemma with knockout mice in standard-- when you get rid of anything entirely from start, it can set off compensatory adaptations that make the resulting phenotype hard to interpret.

*** When glucagon is secreted, it goes to the liver very first.  Glucagon concentrations are significantly increased in the hepatic circulation than in the general circulation, which is one particular of the reasons why it really is considered to act mostly in the liver.  However, Dr. Tony Lam's lab has revealed that it also functions right in the brain to control blood glucose.

**** The amino acid leucine, enhanced on large-protein diet plans, functions in the hypothalamus on mTOR and AMPK pathways, which regulate energy homeostasis (21).  AMPK and mTOR are the cell's main vitality sensing pathways, sort of like leptin and insulin are the main power sensors on the organism degree.  This system appears to be at minimum partly dependable for the potential of large-protein diets to improve human body composition (decrease foodstuff intake, lower fat mass, and increased muscle mass) in rodent models.


Title: Glucagon, Dietary Protein, and Low-Carbohydrate Diets
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