Carbohydrate-Insulin Model
Attack of the Carbs
The Rundown
If you spend enough time learning about nutrition you will eventually hear about the Carbohydrate-Insulin Model (CIM) of obesity in one form or another.
According to the carbohydrate-insulin model, increases in the consumption of processed, high-glycemic load carbohydrates produce hormonal changes that promote calorie deposition in adipose tissue (body fat gain), exacerbate hunger and lower energy expenditure. To fix this, the proponents of the model vilify carbs, point to the glycemic index, and may even go so far as to suggest keto is the only real way to lose fat.
This makes people feel required to cut out all carbs to have any hope of losing body fat. The problem with this is it is misrepresenting how the body truly functions.
Insulin isn’t particularly relevant in body composition in healthy people for fat loss when in a calorie deficit. It can act as a storage hormone when there are calories available to store, yes. But a storage hormone can’t tell your body to store energy that isn’t there.
Similar to “you can’t build a house out of air”, you need some bricks (excess calories) in the mix for it to work. This is part of the law of thermodynamics, you simply can’t build something from nothing. If you are taking in less calories than you burn in a day, you do not have calories available to store as extra body fat.
Don’t take my word for it
The carbohydrate-insulin model has been largely (entirely) discredited at this point and has been replaced by the energy balance model of nutrition.17 The “energy balance model” in nutrition refers to the concept that body weight is maintained when the calories consumed through food intake are equal to the calories expended through physical activity and basic bodily functions, essentially meaning “calories in” must equal “calories out” to maintain a stable weight; if more calories are consumed than burned, weight gain occurs, and vice versa.
Metabolic ward research is very telling in this area…and is the only research that can be considered completely controlled.
In a metabolic ward, patients live in a dormitory-style setting where meals and exercise are controlled for a pre-determined amount of time. This is different than studies in free living people where they leave the research lab and nutritional intake is left up to their choices. Metabolic wards provide strict control over what, how, and when people eat…which is why they give us the most reliable data in nutrition science.
Before I get into it, here are some great overviews on the topic of weight loss and weight gain.1,17 These are some of the best resources explaining how energy balance influences weight change.
Now on to the good stuff.
On to the basics
Ketogenic and other low carb vs low fat studies have painted a rather clear picture that it isn’t carbs that are the issue for otherwise healthy people.
If calories and protein are equated, results will be similar for body composition when attempting to lose weight. This has never been challenged in properly controlled research and has been replicated quite a few times now.
Here are some examples of studies that shed light on the likely true causes of obesity (hint: it’s not carbs or insulin as the primary culprits):
- This large systemic review suggests when we compare calorie-equated high carb/low fat or low carb/high fat diets, we see the same fat loss. Technically, more fat loss on the high carb diet, but this isn’t statistically significant overall.2
- This is a review paper on the regulation of food intake, energy balance, and fat mass.3
- A meta-analysis of the effects of diet composition on body weight.4
- A study showing that carbs and fats are equally fattening.5
- A review paper finding no connection between insulin levels and future weight gain.6
- A study showing that weight loss improves insulin sensitivity to an equal extent when using either low-carb or low-fat diets.7
- A metabolic ward study reporting that fat loss rate actually slowed down with a low-carb diet.8
- A study showing that weight loss was the same in people following a low carb vs low fat diet after 1 year, and that baseline insulin had no effect on weight loss.9
- DOI: 10.1126/science.aav0448
- DOI: 10.1053/j.gastro.2017.01.052
- PMID: 22238401
- PMC: 5568065
- PMID: 11029975
- DOI: 10.1038/sj.ijo.0803500
- DOI: 10.2337/db09-0098
- academic.oup.com/ajcn/article/104/2/324/4564649
- doi:10.1001/jama.2018.0245
- PMID: 7598063
- PMID: 10355026
- PMID: 12543373
- academic.oup.com/ajcn/article/109/5/1328/5480991
- PMID: 31028699
- DOI: 10.1002/oby.22757
- DOI: 10.3945/ajcn.112.036350
- DOI: 10.1093/ajcn/nqac031
- DOI: 10.1101/476655
- PMID: 32597335, 26330303, 15632335, 21494229, 24623974, 33105363, 24113706, 20169360, 32156010, 20035493, 20010118, 24901578, 17200169, 16732018, 30036283, 18583464, 18025815, 21673483, 16446745, 7837950, 28253030, 14505816, 12524670, 28770669, 11874926, 11679448, 19442301, 10896648, 10487375, 25949233, 9738131, 9086690, 31882009, 9216973, 8531622, 28344742, 7762515, 8589778, 27782114, 8567523, 8028510, 27879627, 8379514, 8356979, 17341711, 1852180, 2058588, 18268511, 2361810, 2927298, 15007396, 2718941, 2912014, 23412685, 2667313, 3173455, 16864756, 3337037, 3667068, 15941879, 3661479, 3457234, 17622289, 3457234, 4068964, 4033403, 12704402, 7369151, 4721198, 5412060
But insulin…
Insulin is not needed to store dietary fat and you can still gain fat on low carb diets if your energy intake exceeds your energy expenditure.
One of the ways this happens is through acylation-stimulating protein, which increases lipogenesis (or the creation of new fat) in fat cells and also inhibits hormone-sensitive lipase, an enzyme that promotes fat breakdown.10-12
Another claim the low carb crew makes is if you keep insulin levels lower in general, then fat loss will surely come. This is sometimes known as the breakfast hypothesis (which is one of the reasons many will suggest fasting in the morning). When studied directly, energy balance, health markers, and appetite do not respond differently to multiple weeks of high‐ or low‐sugar breakfasts as long as total calories are controlled.15
Now don’t get me wrong, intermittent fasting where you fit all of your daily intake into an 8-hour window can work just fine for fat loss…it just isn’t due to any magical effects on insulin.
Mistakes were made
Well, that’s all well and good Allan, but the anti-carb crew has shown me studies where insulin and carbs are the devil.
Hold onto your butts, many low carb/insulin studies over-estimate their effect on burning calories due to a common methodology error. Researchers likely know of this, but use it anyway to “show” positive results. You must understand that a lot of these low-carb researchers make money off of selling keto and other low carb diet books and supplements.
The issue involves doubly labeled water calculations failing to account for diet-specific energy imbalance effects on respiratory quotient erroneously suggesting that low-carbohydrate diets substantially increase energy expenditure.13,14 This is just “nerd speak” for using a method of counting calorie burn that gives an erroneously high result. This may or may not be intentional to pad the numbers.
It’s also important to be aware of errors made in previous CIM research that still cause confusion to this day. Ebbeling 2018 is one such example. This study claimed that restricting dietary carbohydrates offers a metabolic advantage to burn more calories and thereby helps patients maintain lost weight. However, analyzing the data according to the original pre-registered statistical plan resulted in no statistically significant effects of diet composition on energy expenditure. Somewhere along the way, it appears the researchers didn’t like the results their original plan was producing, so they decided to change it up.
Furthermore, the large reported diet effects on energy expenditure calculated using the newly revised analysis plan depended on data from subjects with excessive amounts of unaccounted food intakes. Adjusting the data to be proportionate with energy conservation resulted in a diet effect that was less than half the value reported in this paper.18 In other words, it did not end up suggesting any true superiority for the CIM. The promising results in favor of the CIM appear to be due to data manipulation, rather than a true effect.
But seriously, insulin
The idea that insulin traps fat in fat cells, preventing fat loss, isn’t supported either.
In fact, type 2 diabetics and obese people have HIGHER blood levels of free fatty acids, TAGs, and glucose. In interventions where they give drugs that inhibit lipolysis, people still lose just as much fat as those who aren’t on the drugs.
Perhaps most damning are the trials of GLP-1 agonist drugs such as Liraglutide and Semaglutide (Ozempic and Wegovy). GLP-1 mimetics/agonists lead to significantly increased insulin from the pancreas. Interestingly, people given these drugs LOSE fat as a side effect. If insulin response prevented fat loss (in otherwise healthy people in a calorie deficit), you wouldn’t be able to significantly raise it and still see fat loss as a side effect.
Wrap it up
Moral of the story: energy balance explains weight change in nearly all cases.16 There are certain medical conditions that can complicate the matter such as lipedema, edema, and some metabolic diseases. But there is a wealth of research showing calorie deficits work for weight loss every single time in otherwise healthy people.19
You can’t cheat the system through diet. Low insulin diets (keto, Atkins, carnivore, etc.) or conventional diets should be a matter of preference. There’s no significant difference between them for fat loss, and it is possible to gain fat in any dietary pattern if you are taking in more calories than you are burning.
Don’t be fooled into thinking low carb is superior. It can work if you prefer to eat that way, but it isn’t even superior under calorie deficit conditions for those with insulin resistance.
Ultimately, a calorie deficit you can sustain is better than a calorie deficit you can’t sustain. And knowing that you have a choice is a powerful thing.
-Dr. Allan
