In the 1970s and 1980s, dietary fat was the enemy. It was roundly demonised by the media, government and even fitness experts. This led to the flooding of low-fat products into the market, and yet obesity and heart disease incidences continued to climb.
Today, in an attempt to explain the obesity epidemic, it seems that we’ve found ourselves a new scapegoat: carbs.
There have also been claims that as long as you minimise the amount of carbs you consume, you can eat however much fats you require to feel satiated. More on that later though, when we discuss the carbohydrates-insulin model. Well, is the solution to obesity and weight loss really as straight-forward as simply cutting out carbs though?
Brief background on carbohydrates (carbs)
Carbs are not an essential macronutrient, and your body doesn’t need them to survive. That doesn’t mean that they are not good for the body though. Carbs come in many forms such as monosaccharides, disaccharides, oligosaccharides and polysaccharides. For the purposes of being succinct, this article will neither cover specific examples of the various carbohydrates categories, nor the make-up of the categories.
What is important to know is that all carbs, other than fibre, wind up as sugar in the body, and eventually enter the blood, after digestion. Of crucial importance to survival is one particular sugar: glucose. Why is it so important? Well, that’s because your red blood cells can only ever use glucose for energy. Not fat, not ketones — only glucose.
You might be wondering, if that’s the case, then how do people who do not consume carbs survive? It turns out that the human liver has a nifty trick up its sleeves: through the process of gluconeogenesis (GNG), it is able to synthesise the amounts of glucose which is absolutely needed to “keep the lights on”, so to speak.
Insulin and its actions
If you eat carbs, your blood glucose goes up — as blood sugar levels rise, the pancreas produces insulin, a hormone that prompts cells to absorb blood sugar for energy or storage. Other actions of insulin include the:
Inhibition of lipolysis (process by which stored triacylglycerols are broken down and released as free fatty acids into the bloodstream); and
Inhibition of fat oxidation; and
Sparing of glucose for oxidation
Based on the above effects of insulin on the body’s metabolism where it inhibits “fat burning”, some of the most extreme proponents of low-carbohydrate diets have proposed an entire hypothesis of obesity called the carbohydrate-insulin model (CIM) of obesity. Let me explain.
The carbohydrate-insulin model (CIM) of obesity
This hypothesis states that it’s carbohydrate intake, and not total calories, that determines fat loss or fat gain. The model asserts that high insulin from carbohydrates decreases lipolysis, essentially “trapping” fat inside the adipose tissue. Proponents of CIM argue that people therefore overfeed since the other tissues of the body are starved due to the trapping of fat and the inhibition of lipolysis.
While the argument sounds fair and reasonable, it turns out that the hypothesis suffers from a few major pitfalls.
#1 — LCHF (Low Carb High Fat) diets do not produce greater weight loss compared to HCLF (High Carb Low Fat) diets
Following CIM’s line of reasoning, if it were truly the case that it is carbohydrates intake which causes obesity instead of overconsumption of calories, LCHF diets should produce better weight loss results in comparison to HCLF diets when protein and calories are equated. A recent meta-analysis examined all of the studies concerning the issue at hand, and the results were exceedingly clear.
When total calories and protein are equated, the amount of carbohydrates versus fats does not produce differences in fat loss.
In fact, low-fat diets actually produced a slight advantage in energy expenditure and in fat loss!
#2 — Obese people and people with type 2 diabetes have elevated levels of circulating fatty acids
It turns out that the rate of release of fatty acids from adipose is greater in obese people, instead of being lower as argued by the “fat trapping” hypothesis offered by CIM.
#3 — Diets higher in sugar do not cause more weight gain when calories are equated
There have been several studies examining isocaloric (same calorie values) diets with varied sugar intakes, and there has been no difference in fat loss found when calories are equated. In fact, in a study where subjects were provided with every. single. meal. they had to consume by researchers, the group fed with a high amount of sugar (121 grams per day) lost the same amount of fat and weight (!!) as the group fed with a low amount of sugar (12 grams per day).
#4 — Diets high in protein result in better weight loss
Seeing that 50 grams of protein consumption produces nearly the same insulin response as 50 grams of glucose, according to the CIM, high-protein diets should therefore result in obesity. However, we’ve seen that high-protein diets are incredibly useful for weight loss purposes, thereby dealing a huge blow to the basis of CIM.
It’s important to understand that there is no one perfect diet. Diets should always depend on context, and should be what you can adhere and sustain in the long-term basis. LCHF diets can work for people who are better able to maintain a caloric deficit when they stay away from carbs. But…
If the thought of living without eating another plate of pasta depresses the hell out of you, just eat your carbs!
The current available scientific literature supports the notion that HCLF diets and LCHF diets result in the same weight loss results when calories are equated. I hope this article has convinced you to finally, finally eat that piece of bread you’ve been eyeing for the longest time. Let me know if it tastes just as good as it looks.
Thanks for reading! If you want an evidence-based approach to your nutrition, learning how many calories you need for your goals is a good starting point. You’ll like it — I promise!