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The low carb conundrum: What does research say?

freshly baked bread wrapped in a blue kitchen towel

These days it seems that conflicting messages come at us from all different directions. Choose a lucrative career, but make sure it’s your passion. Live life to the fullest, but don’t be irresponsible. Love your body size but don’t get too big, that’s unhealthy. For anyone who’s struggled with weight, this last one can be incredibly painful to hear. 

The confusing advice on weight loss and dieting can make anyone’s head spin. In the last quarter-century, the nutrients blamed for weight gain and glorified for weight loss have varied between fat and carbohydrate. 

Most recently, paleo, keto and Whole30 diets mark a shift toward a low carb/high-fat approach to weight loss. But are they all they’re cracked up to be? Let’s find out.

Low carb just makes sense…right?

While in theory, weight loss occurs when the calories we expend exceed the calories we consume, adding up all those numbers never seems to result in a predictable weight loss. 

This is because, in reality, many factors affect our ability to lose weight and oftentimes, these factors change over the course of our life.  As a result, numerous theories have been proposed on the topic.

According to Gary Taubes, the author of Why We Get Fat: And what to do about it, carbohydrates contribute to weight gain because they boost insulin production in the pancreas.

Insulin, a crucial hormone for growth and survival, helps our cells use energy in the form of glucose (broken down carbohydrate) and store energy in the form of liver glycogen or body fat.

Taubes hypothesizes that with less dietary carbohydrate, insulin production decreases, resulting in less fat accumulation and easier fat breakdown1.

So, low carb = low insulin = greater fat loss.

At least in theory.

Evening the scales

Unfortunately for Taubes, research suggests something else. 

small bowl of oatmeal topped with blueberries in a white bowl

While many studies have compared the weight loss of participants on a general low fat or low carb diet, none have decreased calories equally from fat and carbohydrate while keeping the remaining macronutrients in the diet constant. 

That is until a senior investigator, Kevin Hall, in the Laboratory of Biological Modeling at the National Institute of Diabetes and Digestive Kidney Diseases stepped up to the plate. 

In his, brief but well-controlled clinical trial, Hall decreased the calories from fat and carbohydrate by 800 in two separate groups for 1 week. He then collected the data by controlling everything the participants ate and keeping them in a metabolic chamber to measure exactly how many calories from fat versus carbohydrates they burned2.

Sounds like torture.  But the results?  Invaluable.

Although the participant’s insulin did fall as expected with the low carb diet while remaining constant in the low fat diet, they ultimately lost more body fat with the low fat approach2.

It may be tempting to take this information and determine the case closed, however, that might be a little hasty. 

After all, the study states its own limitation to be the level of carbohydrate reduction. By removing 800 calories worth of carbs, the remaining diet is still comprised of about 30% carbohydrate, far above the percentage in past trials.

For many low carb dieters who reduce their carbohydrate intake much more dramatically, this would seem inadequate for true assessment of low carb benefits.

Hall reasons that he needed to limit the amount of carbohydrate removal in order to be able to equally reduce the fat as it takes up a smaller portion of the average diet to begin with. 

According to NHANES, the average American obtains 33% of their calories from fat, translating into roughly 600-800 calories, depending on their daily caloric total7.

In essence, we eat much more carbohydrate than we do fat and at a certain point, there’s no more fat available to remove! Ultimately, without reducing the two macronutrients equally, it would be impossible to fairly compare them.

So why all the hullabaloo about low carb diets?

For this answer, let us turn to the study of metabolism.

Firstly, we know that for every gram of glycogen (storage form of carbohydrate in the body), 3 grams of water are also stored in the body. With large dietary carbohydrate reduction, glycogen and bound water quickly become depleted5.  This directly leads to rapid, short-term weight loss. 

Secondly, we also know that with very low carb diets a process called ketogenesis occurs, which changes the body’s energy fuel from carbohydrate to fat. From an evolutionary standpoint, this shift allowed us to utilize body fat for energy in times of food scarcity. 

Low carb diets are not easily sustained

So then what’s the problem?

In a meta-analysis of 13 studies looking at the effects of very low-carb ketogenic diets, researchers found that adherence was very poor as the “therapy prominently alter[ed] an individual’s daily habits.” 

Ultimately, the participants in only 1 of the 13 studies stayed within the carb cap of < 50 grams per day4.  For a culture that promotes whole grains, dairy, fruit, and plant-based protein like beans and lentils as essential components of a nutritious diet, adhering to such a low carb lifestyle proves to be incredibly difficult.

So while the diet may be endurable in the short term, the desire for carbohydrate foods eventually wins out, at which point we see a rapid regain of bound water weight.

What we get is a weight loss diet that helps us lose water weight in the beginning and forces us to eat loads of fat with little of our culturally valuable and well-liked carbohydrate foods, resulting in only a slight weight loss advantage when compared to other calorie-restricted diets.  This works if and only if we adhere strictly to the plan.  No wonder so many feel exhausted with weight loss attempts!

woman cutting into a piece of pizza
Photo by Pinar Kucuk on Unsplash

A better plan

In order to maintain the desire for lifelong behavior change, it’s important to acknowledge that many factors affect what we eat and why.  For a deeper investigation into these truths and help in tuning into the body’s natural cues of hunger and fullness, check out Intuitive Eating by Evelyn Tribole and Elyse Resch.

Ready to give up the dieting mentality for good?

Imagine a world where all of us dieters and body checkers gathered up our tireless efforts to be thin and redirected them towards attaining a deep and comfortable satisfaction with the size we are in.

The kind of satisfaction that relishes in the ability to enjoy a wide range of foods from every category and culture and regularly experiences the peace that comes following active movement. Few traits are more attractive than this.

It is true that our world currently rotates with a different goal in mind, one of thinness rather than health, but slowly we can make it different.

References:

  1. Liebman, B. (2016, January). Scaling back: scientists search for keys to weight loss. Nutrition Action Health Letter.  43(1) 3-6.
  2. Hall, K., Bemis, T., Brychta, R., Walter, M., Walter, P., & Yannai, L. (2015). Calorie for calorie, dietary fat restriction results in more body fat loss than carbohydrate restriction in people with obesity. Cell Metabolism, 22, 427-436. http://dx.doi.org/10.1016/j.cmet.2015.07.021
  3. Gibson, A., Seimon, R., Lee, C., Ayre, J., Franklin, J., Markovic, T., Caterson, I., & Sainsbury, A. (2014). Do ketogenic diets really suppress appetite? A systematic review and meta-analysis. Obesity Reviews, 16(1) 64-76. doi:10.1111/obr.12230
  4. Bueno, N., Vieira de Melo, I., Lima de Oliveira, S., & Rocha Ataide, T. (2013).  Very low carbohydrate ketogenic diet v. low-fat diet for long-term weight loss: a meta-analysis of randomized controlled trials.  British Journal of Nutrition, 110(7) 1178-1187.  doi:10.1017/S0007114513000548
  5. Roberts, S., & Das, S. (2015). One strike against low-carbohydrate diets.  Cell Metabolism, 22, 357-358. doi:10.1016/j.cmet.2015.07.022
  6. Sackner-Bernstein, J., Kanter, D., & Kaul, S. (2015). Dietary intervention for overweight and obese adults: comparison of low-carbohydrate and low-fat diets. A meta-analysis.  PLOS One, 10(10) 1-19. doi:10.1371/journal.pone.0139817
  7. US Department of Health and Human Services/Centers for Disease Control and Prevention. (2000). Intake of calories and selected nutrients for the United States population, 1999-2000. (pdf)

This post originally appeared on the Moore Family Center Food Coach blog, which is written by OSU dietetic interns.