Low Fat Diets are Better Than Low Carb Diets and the Source of Media Nonsense

This just in! Its blowing up the news and social media! A new study has just found that low fat diets are better than low carb diets for weight loss. Wait, what? Low fat is better than low carb? But haven’t these eggheads been saying that low carb is better for a few years now? Why can’t they make up their minds? The answer is complicated but I think it’s best to start by breaking down the most recent study and then I’ll explain to you why there appears to be confusion and why the news is a terrible source of getting health and medical news. It may also be a terrible source of getting any news but that’s for a different blogger and a different time.

Nowadays, diets come in different flavors, but usually fall into a low carb or low fat category. While low-fat diets were popular in 90s, carb restriction has regained popularity in this century. Advocates of low carb diets claim that there is a decrease in insulin secretion which causes more fat to be burned and greater body fat loss than low fat diets. I, myself was converted to this religion as the data came out in support of the idea. When I first set out on my weight loss education campaign, I was a zealot for the idea that the law of conservation of energy could not be broken and that a calorie is a calorie. In other words, if you burn more than you take in you will lose weight. But I was then swayed by research showing that low carb is the way to go (see my post on the subject here) that suggested that low carb diets have more favorable impact on metabolism. Then the news hit of the most recent study that, according to the headlines “proves” that low fat is better.

So what’s the deal? Which is better? Before we can tackle that question we first have to look at the recent study. The researchers took 19 obese adults and confined them to a metabolic ward of the NIH research hospital on two separate stays. For the first five days of each visit they ate a baseline balanced diet. Then for six days, they were fed diets containing 30% fewer calories, achieved by cutting either only total carbs or total fat from the baseline diet, while eating the same amount of protein. They switched diets during the second visit. They also used a mathematical model to take this data and make computer based predictions about what the long term results would be. At the end of the study the low fat diet led to the loss of an extra ½ pound of fat. The mathematical model predicted that the low fat diet would lead to about 12 pounds more fat loss than low carb after 6 months.

It would seem from these results that low fat diets are better than low carb diets. But before you come to that conclusion you need to consider some caveats. First, this study was designed for the purpose of better understanding the physiologic responses to changes in diet composition. It was not designed nor did the authors of the study intend to determine which diet is better for weight loss in a real world setting. Second, you can only expect the results of this study if you follow precisely the diets and exercise prescriptions used in the study. This was not a real world setting and doesn’t account for the ease of sticking to the diet. It did not evaluate how well the diets can be adhered to outside of the hospital. Third, there weren’t so many patients studied. Fourth, the study relies on a mathematical model and mathematical models don’t always adhere to reality (just ask the Weather Channel).

Based on this information, If I was writing the headlines for the news outlets I would say the following

“New study finds that if you are locked in a hospital with your meals and exercise strictly controlled you will lose more body fat with a low fat diet compared to a low carb diet based on computer models”

It may go without saying that writing news headlines is not a strength of mine. The point is that when you read a headline based on the actual results of the study you are unlikely to read the article but if the headline reads:

“For fat loss, low-fat diets beat low-carb diets handily, new research finds “

like the LA Times said, or

“Low-Fat Versus Low Carb:  Which is better for weight Loss?”

like Newsweeks said or maybe,

“Low-fat diets ‘better than cutting’ carbs for weight loss”

like the BBC said, you are more likely to read the article and see their advertisements, which is their ultimate goal, with informing you being a secondary priority.

You must remember that science is not a centralized monolithic edifice that issues edicts from on high. Science is a method. For those of you who forgot your middle school science classes, the scientific method includes the following steps as described by livescience.com

1. Make an observation or observations.
2. Ask questions about the observations and gather information.
3. Form a hypothesis — a tentative description of what’s been observed, and make predictions based on that hypothesis.
4. Test the hypothesis and predictions in an experiment that can be reproduced.
5. Analyze the data and draw conclusions; accept or reject the hypothesis or modify the hypothesis if necessary.
6. Reproduce the experiment until there are no discrepancies between observations and theory. “Replication of methods and results is my favorite step in the scientific method,” Moshe Pritsker, a former post-doctoral researcher at Harvard Medical School and CEO of JoVE, told Live Science. “The reproducibility of published experiments is the foundation of science. No reproducibility – no science.”

The end result is that one study almost never proves anything.  All the evidence is collected, reproduced, and compiled together to get results that, if consistently proven in multiple environments under differing conditions and refinement, can be considered a fact or a scientific law. Very few hypotheses make it to the glorified status of scientific law.

If you take the fact that one study almost never proves anything and that this study is not something that is generalizable to real life we are left in an unfortunate place where the question of low cab vs. low fat remains an open one.

What we can do is approach the subject with intellectual honesty and create a conclusion based on the best knowledge we have at the time.  Right now, there is a lot of evidence supporting low carb diets being the most effective way to lose weight but the theory has not been proven unequivocally. This is due to how complicated human metabolism is, how many variables need to be controlled for, how difficult it is to measure metabolism, and how much it would cost to systematically study the topic. Any book or news article that says clearly that one is better than the other is being disingenuous. Research can suggest that one is better but only with so much certainty. Be skeptical of everything you read that makes it sound easy or simple.

The end resulf of all of this is the unfortunate situation where, as new data comes out, recommendations change in response. This can be confusing but it is an unavoidable reality.

In reality, I don’t think the question should be which diet is better, the question should be which diet is better for you.  Which diet can you stay on for the rest of your life? Which diet can you afford? Which diet is the easiest to follow when you’re strolling the aisles at the grocery store?  And so on. The reality is that neither low carb nor low fat diets work if you stop following them. So find the diet that best fits your personality, lifestyle, and weaknesses and stick with it. If it doesn’t work or you can’t maintain it, try a different one. Keep trying, don’t quit and you’ll eventually find something that works with you.  The key is that you have to stay on it.  I promise, if you are patient and stick with it, it will work eventually.