Are Low-Carb Diets Effective for Weight-Loss? 

What’s interesting to note about most studies examining low-carb diets is that calories are often not controlled for in these studies. In research, we refer to this as ad libitum diets - meaning participants can have as much food (calories) as they’d like.

Given that calories are often not controlled with these diets, why is it that participants still manage to lose weight if they aren’t counting calories? After all, don’t calories still matter when it comes to weight loss or is it really more about the quality/composition of your diet?

According, proponents of low-carb diets the ‘calories in vs calories out’ model for weight-loss is deeply flawed. Instead, advocates of low-carb diets as well as intermittent-fasting alike, insist that calorie-controlled diets are not necessarily the key to weight-loss - instead it’s the management of a hormone called insulin.

Unlike the traditional ‘calories in vs calories out’ explanation for weight management which insists weight gain is due to an energy imbalance in which calories consumed is greater than calories expended, the carbohydrate-insulin model insists that an imbalance in hormones, specifically insulin causes weight-gain. 

Insulin is a hormone secreted by the pancreas during digestion/absorption of nutrients. Insulin secretion is highest after consuming carbohydrates compared to protein or fat. While eating protein-containing foods causes insulin to rise to a lesser extent, consuming fat has a negligible impact on insulin release. 

What we know about insulin is that it’s an anabolic hormone, in other word it promotes the synthesis of protein and glycogen (the storage form of carbohydrates) while inhibiting the breakdown of stored body fat. 

Insulin is one of the primary hormones helping to regulate blood sugar because it essentially is the ‘key’ that unlocks a cell and allows glucose to be used as energy inside that cell. However, it’s believed that when insulin is chronically elevated due to eating frequently and/or eating a high-carbohydrate diet - this inhibits stored body fat from being used as energy. 

Another way to think about it is comparing your carbohydrate stores to a refrigerator and your fat stores to a deep freeze. Stay with me, here. Let’s pretend you are hungry and want something to eat: is it easier to grab something from your kitchen’s refrigerator or walk out to your garage or down to your basement and pull something from the deep freeze? 

Obviously, pulling food from the refrigerator is easier. 

While the insulin-carbohydrate hypothesis is indeed a hypothesis there are plenty of clinical examples that demonstrate the role insulin plays on weight management. Take for example, the type I diabetic - these individuals are deficient in producing insulin, therefore, require insulin injections via an insulin pump. Prior to a person being diagnosed with type I diabetes one of the early signs of insulin deficiency is rapid weight-loss.

Without insulin being pumped through the body, blood sugar can’t be stored and/or utilized for energy causing the body to shift to burning fat-hence the dramatic weight-loss. The only way weight loss can be restored is through insulin injections.

The inverse of type I diabetes is type II diabetes, a condition in which the body produces excess insulin in an attempt to compensate for insulin resistance (i.e. the key that allows glucose to enter the cell is broken). In this scenario, when the body is producing excess insulin in the presence of carbohydrates, weight gain occurs. We also know that insulin resistance accompanies several other conditions like PCOS and Metabolic Syndrome which makes weight-loss for these individuals a challenge. 

While the carbohydrate-insulin hypothesis seems logical, there other factors at play that contribute to individuals' success on low-carb diets.

Reducing carbohydrates may also increase energy expenditure. A 2021 meta-analysis published in the Journal of Nutrition showed that energy expenditure slightly decreases in the first two to three week of a diet compared to higher carbohydrate diets. BUT as diet adherence continues, studies show that energy expenditure increases on low-carb diets compared to higher carb diets. 

A 20 week controlled feeding trial, showed that participants on a low-carb diet (consisting of 20% calories from carbs) increased their energy expenditure by 250 calories more than participants weight-matched on a high-carb diet (consisting of 60% calories from carb). For both diets, participants received the same types of carbohydrates and calories were adjusted for weight-maintenance of participants. 

One notable difference between low-carb and high-carb diets is their impact on hunger, fullness, and subsequent eating. Most studies on low-carb diets don’t restrict calorie intake but instead let participants eat as much as they like (aka ad libitum intake). Despite calories generally not being limited on low-carb diets participants still spontaneously end up eating less than on high-carb diets. 

There are a couple different factors that explain this phenomenon. On one hand, low-carb diets are typically higher in protein and we know protein is the most satiating macronutrient. 

In addition, diets like keto which is a VLCD (< 20 grams per day) tend to be limited in protein but are believed to increase satiety once ketosis is reached. Ketosis is a metabolic process that occurs in the absence of glucose. When glucose is unavailable, the body switches to burning fat for energy which produces ketones. Ketones are known to have an appetite-suppressing effect. 

Finally, low-carb diets can improve blood sugar control especially in those with insulin resistance. Low-carb diets may reduce hunger because they lead to fewer episodes of what’s called rebound hypoglycemia. This typically happens when the pancreas overproduces insulin causing blood sugar levels to plummet too quickly. Consequently, this can increase hunger even though you may have just finished eating a bowl of granola or another high-carb food. 

Okay, so now you might be thinking this all sounds great, sign me up for keto or the Atkins. But before you do that,  let’s examine some of the cons of low-carb diets. While yes, there is plenty of research to support low-carb diets being an effective strategy for weight-loss, one has to consider the sustainability of low-carb diets, especially the most restrictive forms of low-carb diets.

While macronutrient ratios are an important aspect of all low-carb diets, the quality of the macronutrients (carbohydrate, protein, and fat) consumed is also an important factor to consider.

In studies examining the effects of low-carb diets on markers of metabolic health such as cholesterol, we find that generally a low-carb diet worsens your bad cholesterol, known as low density lipoprotein ( LDL) and increases total cholesterol. This is most likely a result of low-carb diets being higher in saturated fat. Saturated fat is considered an unhealthy fat present in in animal products and tropical oils. And having High LDL levels are risk factors for both fatty liver disease and cardiovascular diseases. 

In addition, low-carb diets which limit carbohydrates to less than 26% of calories tend to be extremely low in plant matter. Tons of research has shown that plants, particularly fruits and vegetables are linked to lower mortality rates and overall improved health. 

Plant foods also are an abundant source of fiber. Dietary guidelines currently recommend that adults consume between 25-38 grams of fiber per day. Those on low-carb diets would find it extremely difficult to consume even 1/2 of the recommended amount due to carbohydrate restrictions.

For example, on the keto diet you are allowed only 20 grams of carbohydrates - if you consume 1.5 cups of raspberries, which are one of the highest fiber fruits, you’d only get 12 grams of fiber in your diet but would also max out your carb intake for the day. 

Plants are also rich in antioxidants and micronutrients (vitamins and minerals) which are essential for preventing nutrient deficiencies and promoting overall health.

Research supports that a very low and low carbs diet can be an effective strategy for losing weight especially for those with insulin resistance or other metabolic conditions which contribute to blood sugar imbalances. However, some individuals may find it hard to follow due to taste preferences, cost, or other factors.

Most people can achieve weight-loss and improve overall markers of health by eating a moderate amount of carbohydrates and focusing on improving the overall quality of all macronutrients including carbohydrates. 

Replacing refined grains, desserts, and added sugars with whole food sources of carbohydrates like low-fat dairy, fruits, vegetables, whole grains, and beans is one of the best ways to improve the carbohydrate quality of your diet. 

Also, consuming fewer calories than you take in is still the most important factor driving weight-loss. But that’s not to say your hormonal health doesn’t play a role. 

Insulin along with many other hormones is clearly involved in regulating blood sugar, appetite, and subsequent calorie intake. If you believe you may have hormonal balances making it difficult to lose weight, talk with your doctor or a dietitian before you decide to embark on the low-carb lifestyle. 

Cheers!

Alisa