MG, thanks for the offer! Here are my top two questions.
1) To what extent can the body store dietary fat as adipose tissue in the absence of dietary carbs? In plain language, can humans gain significant body fat on a VLC diet? I've seen both points of view on this forum and would really like to know.
2) What are the metabolic effects of sugar alcohols like xylitol, sorbitol, and maltitol? There's the famous laxative effect, but surely there must be something else at play, at least some kind of skewing of intestinal biota towards the strains that can tap this fuel source.
I could grill you all day with questions but I will restrain myself to those two for now. :)
Thank you so much for your generous offer, and I hope you're not being overwhelmed by the questions you've generated.
I've got two questions dealing primarily with fats.
1) I have a hard time explaining fat metabolism to people when trying to explain why eating fat won't make you fat. So if you could please describe what the body does with dietary fats with an emphasis on why they do not immediately form adipose tissue in the body.
2) I've seen the hypothesis quite a bit that the body stores excess toxins (that is, beyond what it can filter out and excrete) in adipose tissue as a protective measure. I haven't been able to confirm this anywhere, though. Is there any validity to this theory? If so does the body also store nutrients in a similar manner if dietary intake is abnormally high for a brief time, in order to utilize them later.
Thanks again for answering all these questions.
@Darthash Caffeine works principally by virtue of the fact that it (and it's buddy found in chocolate, theobromine) looks a lot like the business end of adenosine. Adenosine is a compound composed of a ribose sugar and an adenine nucleic acid, both of which are most typically found making up part of our RNA and DNA. Adenosine levels help the body to keep track of how much excitement/available energy is necessary by rising when we need to calm down (or at least when the body THINKS we do).
Since adenosine is used to signal for a wide variety of processes, it's tough to tell you about specifics of what caffeine's mimicking it does (although if you REALLY care, we can discuss it), so just think of it in two ways:
1) Sometimes there are proteins which break down adenosine normally, but whose active site (the place where most of the actual chemistry happens, not that the other bits aren't important in less obvious ways) will allow caffeine to enter. When these enzymes are what's known as "highly substrate specific", even the slight differences between similar molecules can prevent the normal chemistry from occurring. Normally the first step in breaking down adenosine is pulling off an amine (NH2) group, but caffeine has a methyl (CH3) group in that spot, and methyl groups are tough little buggers. Thus, you don't break down adenosine like you should.
2) There are other proteins which sense levels of adenosine which caffeine can sometimes fit into. When it does, it may (depending on the protein) cause the conformational change necessary to signal "adenosine here", or it may just hang out in the active site, preventing adenosine from being sensed. Either way, adenosine levels are sensed as something other than they are.
The net result is that the body puts itself in a heightened state of alert, releasing extra fat from your adipocytes, but also raising cortisol levels in preparation for a fight or flight decision.
I'm going to have to keep these shorter if I want to get to all of you.
Variations in individual workout routine and genetic predispositions make it difficult to say just what might be happening to you, but you're not alone in recovering faster when you have more carbs in your diet. Why? It could be a lot of things; not enough calories, expecting glycogen repletion to be more rapid than is possible under a VLC diet, or even psychological dependence (how long did you internalize the "carbs are fuel" notion before you went primal? Years, I'm sure). Self-experimentation to find your macronutrient ratios is key, since we frequently CAN'T disentangle the thicket of confounding variables like we'd wish. One thing to note, however, is that VLC diets with periodic carb feeds cause "glycogen supercompensation" -- the storage of MORE glycogen than you would be capable of under consistent carb intake.
As far as "eat all the carbs you see as long as there's not a drop of fat, and you won't gain weight" goes, it's hogwash. When you have tons of glucose enter your system, your liver first makes glycogen. When that runs out, it checks blood glucose levels and puts out as much blood glucose as it thinks you'll be able to handle (this may be inaccurate if you have problems with insulin sensitivity). After that, the glucose doesn't hang around. It gets converted to, guess what, FAT! Now you have lots of fat AND a hormonal environment conducive to its storage. At this point, your body doesn't much care whether or not the fat was endogenous (made from sugars) or exogenous (from dietary fat). Sure, active -- and more importantly, insulin-sensitive -- young people may easily tap the fat that they're storing (so they don't "get fat"), but rest assured they are storing it.
Probiotics are modestly beneficial to someone eating properly (not tons of fermentable carbohydrate in this case), but are of great benefit to people with depopulated or overpopulated (with the wrong beasties) guts. Periodic intake of a suite of good beasties helps make sure that there's some diversity in your gut and no one group gets too prevalent. For example, too much Heliobacter pylori and you get cancer, too little -- it's now emerging -- and your immune system suffers. Most of the bugs in a probiotic fail to adhere to the intestinal wall (or die in their acid bath on the way in), but a few get a toehold and start raising families.
I'm inclined to tell you that the slowed gastric emptying and increased satiety (thus causing fewer carbs to be eaten in the first place) are worth any insulinergic effect the proteins may have. When sugar is parceled out more slowly, the area under the insulin curve tends to be smaller anyways. Besides, insulin SPIKES aren't bad in the absence of pathology, CHRONICALLY RAISED insulin is bad.
And, as you suspect, this is pretty much a moot point in someone eating ~100g carbs a day. You're just not getting much of an insulin response to that, for a variety of reasons I'll enumerate if you care.
Much of it has to do with the fact that the enzymes responsible for getting fat where it needs to go and breaking it down (mostly the first) aren't being expressed highly yet, so you're having a tough time getting energy where you need it and moving the fat along through different parts of the system (not enough bile salts in your gut included). You haven't needed them this much before, and the body abhors waste! As you sustain the different macronutrient ratio, your body adjusts, pulling resources from making proteins that deal with sugars and allocated them to fat metabolism. This is an example of the "gene reprogramming" that Mark talks about.
Appreciate your response.
Truly awesome to have someone to explain stuff with some straight-up science! Here's a quicky: Is there any chemical explanation behind the CW that nutrients are more easily absorbed just after a workout (or just a scam by manufacturers of protein powder)?
1. There's quite a bit of controversy over vitamin D, and the science isn't all in on the issue. That being said, given that hunter gatherers the world around seem to go out of their way to eat foods high in vitamin D whenever they aren't making a TON themselves from sunlight, I'm strongly given to suspect that we benefit from high D consumption. That being said, I make sure to eat plenty of A along with my D, since a number of unpleasant things happen when one gets too low while the other is high.
2. Oxalates aren't likely to make you fat. They are, however, stealing minerals from you that you'd otherwise like to have. In general, however, they're destroyed reasonably well by cooking, so I would just make sure not to eat too many raw, oxalate-containing foods if you're worried about it.
3. I will be surprised if somebody doesn't find a compound which induces fructose malabsorption soon given all of the bad press fructose is getting. Imagine having lactose intolerance but for fructose. You'd kick your sugar habit in a hurry. If I had access to a high-throughput chemical screening lab...
1. We store fat reasonably well in the absence of insulin (although certainly not as well), but we also burn it VERY readily in the absence of insulin. That's the more important part, in my opinion. Because of this, it's tough to "get fat" since you'll tend to just pull the fat out of your adipocytes and burn it (for heat or by inducing activity) rather than keeping it locked up. "Getting fat" is a largely hormonal event that involves your fat cells absorbing fats better than (and before) other parts of your body and then not giving them up.
2. Sugar alcohols probably cause some slight disruption of gut floral balance and they also cause loss of adhesion to the intestinal wall. It would take a lot of them, however, to be much of a problem.
That said, however, there are TWO ways that we sense the need for insulin, only one of which is dependent on blood sugar. The other is by starchy/sweet tastes in the mouth, which cause an initial "get ready" surge of insulin. This may or may not hurt your weight loss depending on how well your body responds to this insulin.
@ Greg B
1. You eat fat, which goes to the gut and is absorbed. The small and medium-chain fats go straight to the liver, completely bypass the carnitine shuttle which normally makes them wait in line and get rapidly metabolized into ketones for energy. These are tough to store, so you tend to just burn them for heat if you don't use them.
Long-chain fats have more of a journey. They enter the lymph system in lipoprotein casings called chylomicrons and enter the blood, being delivered to a variety of tissues. If your body doesn't need them for energy, it stores them, but as I described above, it also accesses them very easily as long as insulin levels are low. This easy access means it takes any excuse to use them, making it hard to "get fat" eating fat. "Getting fat" requires that you completely overwhelm your body's ability to fritter away excess calories (which is quite substantial) OR that you cause a hormonal environment which makes withdrawals difficult, such as chronically elevated insulin.
2. Yes, we do store some toxins in our fats. In general, we try to use enzymes like cytochrome p450 to make toxins A) less toxic and B) highly water soluble so that we can just excrete them in our urine, but when we are unable to do this for any of a number of reasons we do store them in our adipose tissue. Since glucose can cause highly undesirable glycation reactions in high enough concentrations (i.e. be toxic), we store it as fat instead of allowing it to circulate in large amounts.
We also store some nutrients, but only the lipophilic (hydrophobic/fat-soluble) nutrients which can be stored that way. A, D, and K are the principal ones, although we may store some phytochemicals in our fat as well (this, actually, because they are toxins in large amounts as well). We also, of course, store energy in our adipose tissue.
Insulin sensitivity spikes post-workout for about 1-2 hours, remaining modestly elevated for some time after that. Since insulin is responsible for sugar and amino acid uptake by your muscles, greater insulin sensitivity means greater capacity to uptake nutrients. Other factors are at work as well, like increased blood flow to the muscles, but insulin sensitivity is the major culprit.
That said, I wouldn't get too neurotic about post-workout eating. The benefit is pretty modest, and healthy, insulin-sensitive individuals will refuel their muscles just fine no matter when they eat.
Greatest thread ever. So informative.
MG: re your reply on vitamin D. What of the recent research that suggest too much vitamin A negates the benefits you would receive from vitamin D? It's recently been on Mercola and I think even the Vitamin D Council spoke of it as well?
Anyway, I'm heading into a science degree next year and just wondering if I should major in nutrition & nutraceutical science or biomed science. (Not doing biochem because the extra math I'd need - calculus - is not going to happen lol.) What were your favourite subtopics within the biochem category?