There is an argument that is increasingly being made, that fat cannot store fat. While we agree carbs may be the biggest issue for some, not all, when it comes to reaching your fat loss goals, fat DOES store fat. When you think about fat loss many say it is all about hormones, and others claim it is all about calories. That is a silly argument because both hormones and calories matter. When it comes to fat, it is both rich in calories, AND it impacts hormones that signal fat storage.
For many people however, it may be the combination of fat and carbs mixed together in meals that is the major culprit.
The idea that fat does not store fat is an old argument. It is the basis of one of the most popular diet books ever, The Atkin’s Diet. This idea comes from the fact that fat, by itself, has little impact on the major fat storing hormone insulin. This is true….kinda…..we will get to that in a minute.
It also makes the assumption that insulin is the ONLY fat storing hormone and that calories don’t matter at all. While we would agree hormones are the drivers of how much we eat, what we desire to eat, and whether that fuel is stored as glycogen, muscle, or fat, to say calories don’t matter is simply not true. What many also do not realize is that there are other hormones that store fat besides insulin and that without a calorie surplus fat will not be stored period.
Review of insulin
Insulin is a fat storing hormone because it increases the major fat storing enzyme in the body called lipoprotein lipase (LPL). It also does two other nasty things that make fat loss very difficult when it is around in larger amounts: decrease hormone sensitive lipase (HSL) the major fat burning enzyme AND slow fat oxidation by suppression of CPT-1 (the rate limiting step in fat burning).
So, decrease insulin and fat storage is slowed while fat release and burning is sped up. You can decrease insulin by decreasing calories or by decreasing carbs (all else being equal a lower calorie diet is typically a lower carb diet than one was eating before, and a lower carb diet is a lower calorie diet too. People seem to forget this when debating this issue. Since carbs are the major promoter of insulin, many people simply say cut carbs and that’s that. This is where those who subscribe to the “fat can’t make you fat” stop their story.
3 fat storing hormones you probably never heard of
What many fail to realize is there are at least 3 other fat storing hormones and probably more we will find out about at some point. Not to mention all the other hormones like estrogen, cortisol and others that influence fat burning indirectly.
One of them is called acylation stimulating protein (ASP). Where insulin is induced by carbs, ASP is induced by fat AND, in an unfortunate fat storing feedback mechanism, both ASP and insulin stimulate the secretion of each other. So, in an indirect way, fat does stimulate insulin & insulin stimulates a fat storing helper ASP.
The third fat storing hormone is a gut produced signaling molecule called glucose-dependent insulinotrophic peptide (GIP). GIP is induced by both carbs & fat and to a much lesser extent protein and fiber. GIP has its own fat storing action on LPL AND causes more insulin to be released (here again fat can result in indirect insulin secretion).
The hunger hormone ghrelin (the intermittent fasting crowd is likely going to dislike me for this one) is also a fat storing hormone. Ghrelin is released when we forgo food. Not only may it directly induce hunger AND cravings for sugary fatty and salty foods (research here & here & here), it has direct actions on the hypothalamus aiding fat storage (research here) and also increases the action of LPL and even results in more LPL being made so that when you do eat (research here)……you get fatter quicker. This is because ghrelin increases the mRNA expression of LPL.
Ghrelin should probably be called the yo-yo weight gain hormone, and those who practice eating less and exercising more are unwittingly raising their ghrelin and fat storing potential. The fact that ghrelin has some positive effects, like raising HGH, does not change these negative consequences. If and when fasters and low calorie dieters resume normal eating, fat gain comes and comes quickly. And this may largely be due to ghrelin (Ever meet anyone coming off strict diet restriction and getting fat quick? Is that ghrelin at work?)
And calories of course
Obviously calories matter and they matter a lot. Fat is the least thermogenic, the least satiating and the most calorie dense of all the macronutrients. I know this will come as a surprise to many in the high fat low carb community especially as it pertains to their beliefs about fats satiating potential. Fat combined with protein is very satiating. Fat alone, not so much. Once in ketosis, ketones are very satiating as well, but fat and ketones are not the same thing. For more on this science read this blog.
Add carbohydrates to fat and you may be asking for the worst of all worlds. These two foods combined are highly palatable and animal research suggest this combo is a primary signal for overeating. In other words, this highly enjoyable food combination causes us to crave and consume more foods like this. (research here and here)
It looks like this happens in humans too (studies here, here and here). These studies show humans who are isolated in a metabolic chamber and given free access to highly palatable foods, do what the rats do; they overeat by huge margins. The participants in these studies end up eating close to a 1,000 calorie surplus and gain on average 6 pounds in only 7 days. While the metabolism does ramp up its calorie burn as well, you can see something very detrimental happens when these types of junk foods are chosen.
The worst fat storing combination (fat & starch/sugar)
So, what does all this mean? It means both carbs AND fat cause fat gain, and when they are combined together it is far worse than eating them alone.
Glucose-dependent insulinotrophic peptide (GIP):
Here is how the story goes: eat carbs and you release insulin…….you also release GIP which means a double hit on LPL (both insulin and GIP increase LPL’s fat storing action). BUT, GIP also causes the release of insulin itself. In fact, GIP may be more important than even glucose in raising insulin (this is one of the reason the same amount of glucose given directly into a vein causes less insulin secretion than if it were eaten).
One thing to know about GIP is that its fat storing potential is really most sensitive to glucose. In other words, fat releases GIP but it appears the potent fat storing activity of GIP kicks in strongly only with hyperglycemia (high blood sugar). So, fat and carbs together cause more GIP release and greater fat storing activity than either alone.
At this point you may be a little bit confused so here is the story for GIP in bullets:
- Carbs Alone= insulin= fat storing
- Carbs Alone= GIP= Insulin= Fat storing
- Fat Alone= GIP without hyperglycemia= a little insulin= Little fat storage
- Fat with carbs= GIP plus hyperglycemia= excessive insulin= excessive fat storing
- *keep in mind this is only when you are in calorie surplus for the day
Aceylation Stimulating Protein (ASP):
ASP is stimulated directly by fat. It is stimulated indirectly by carbs because insulin stimulates ASP as well, and then ASP returns the favor by stimulating insulin. Interestingly for women, progesterone is a stimulator of ASP as well which is useful information for menstrating females who might want to decrease their fat and carb intake during the luteal phase of their cycle (menstrual phase occurring between ovulation and onset of menses). Here is the story of ASP in bullets:
- Carbs Alone= insulin= ASP= Fat storing
- Fat Alone= ASP= Fat Storage
- ASP= insulin= Fat Storage
- Fat with carbs= Double ASP= double insulin= excessive fat storage from independent action of both ASP & insulin
- progesterone= ASP= fat storage
- *keep in mind this is only when you are in calorie surplus for the day
Ghrelin is a hunger hormone released from the stomach that travels to the brain and induces hunger. Ghrelin has also been shown to do a few other things not beneficial to dieters. Ghrelin causes the brain to crave sugary, salty, and fatty foods, so is also implicated in cravings.
Ghrelin also makes us more efficient at storing fat once we do eat. This is because ghrelin stimulates messenger RNA (mRNA) activity of the fat storing hormone LPL. For those who are not biochemists, mRNA is how the genes replicate the proteins they encode for. So, mRNA makes proteins, and the more mRNA activity you have, the more protein you make.
In the case of ghrelin, it stimulates the mRNA to make more LPL (the major fat sotring enzyme), and therefore makes you far more likely to store fat quickly and efficiently once you resume eating. So dieters and fasters beware. Ghrelin also directly stimulates LPL activity :-(. While ghrelin does have some beneficial effects, it may elevate HGH, we regard ghrelin as largely negative for your fat burning goals.
It is important to put all of this stuff in context. Fat loss is not just about hormones, and it is not just about calories. It is about both. It is also about the compensatory reactions created that lead to sustainable lifestyle changes or short term dieting & weight regain.
The other thing to realize is that we are all different, so all of this information cannot simply be stated as true for everyone. There are those who can fast and not have any negative impact from ghrelin and get and stay extremely lean. There are those who can eat doughnuts and burgers and not have any seeming negative fat storing impact from GIP and ASP. We would say these types are in the extreme minority.
One question that nags many in the nutrition world is the glycemic index issue. They often wonder how this relates to the fact that fat slows the release of sugar into the blood down and therefore lowers the glycemic index. This is true and is useful to know especially for those who are extremely carb sensitive.
So, yes it is true fat added to a simple sugar will lower the speed at which blood glucose rises, and this is especially important for the very insulin resistant and diabetic. The point is the body will still need to deal with the entire glucose load and fat load in the food. And, due to all the hormonal effects mentioned above, this creates a perfect fat string atomic bomb. So, it may be more beneficial to do things this way for someone who is diabetic, but it is not ideal and will still likely make you extremely fat if done on a regular basis.
So, our advice after considering all this information is the following:
- Both fat and carb have fat storing potential through several mechanisms.
- Choose fat over starch/sugar when given a choice. In other words, choose bacon for breakfast over corn flakes.
- Never combine fat and sugar/starch (doughnuts, pizza, burgers, chips and guacomole, granola, cereal and whole milk, full fat yogurt and sweet preserves, etc.).
- Very high fiber carbs with low starch are probably not an issue, although they can be for some (celery and peanut butter, healthy hemp bread and avocado, mixed nuts, etc.).
- If you are extremely insulin resistant or diabetic and you must do simple carbs, then you may want to add fat. This may save you from having to have a leg amputated one day, but it wont make you thin.
- Going without food raises ghrelin and enhances your ability to store fat later so be careful when fasting or doing extreme diets.
- Protein and fiber have minimal impact on fat storing hormones (the insulin protein issue can be complicated and a topic for another blog) and satiate you. And both activate GLP-1 which is GIPs alter ego.Want a little more on the rationale and science behind this concept? Check out this BLOG
- Combining fat and starch or sugar is not going to make anyone fat if they do not achieve a calorie surplus. Kind of common sense for those of who work in this field, but the hormonal mechanisms are useful for those convinced there is some advantage to be had with adding fat to things. What this information shows is the combination makes us more likely to do that and the hormonal mechanisms assure those calories are stored away as fat.
- None of this matters in the context of the individual. It does not matter what you are eating if it is working for you. Nothing is absolute in health and fitness.
**last update 1/1/2017**