Low-fat Diets Don’t Work

Finding Weight-Loss Success

Conceptually, gluten free, the Paleo approach and ketogenic diets are very easy. These diets inherently take the decision-making process out of the equation because there is no middle ground— the food is either on your diet or it’s not. You don’t have to measure portion sizes, log calories or determine if you have to eat less at dinner to make up for a lunchtime splurge. The desire for a simplistic and concrete answer to weight loss has led to a decades-long battle about the best macronutrient composition for weight loss. Over the past 100 years, we’ve ping-ponged back and forth between high-carbohydrate, low-fat diets and high-fat, low-carbohydrate diets. Experts offer equally persuasive arguments for both ends of the spectrum— either low-fat or high-fat. In an attempt to determine which diet is best for weight loss, one of the latest studies collected and analyzed the research on low-fat and high-fat diets.

Study: Low-fat Diets Don’t Work

The Study

A systematic review and meta-analysis, which combines the results of several studies, published in the journal The Lancet, compared the results of intervention studies > 1 year in length where participants were placed on low-fat diets, low-carbohydrate diets, other high-fat dietary interventions or they continued consuming their usual diets. The authors included 53 studies in their analysis. Low-fat diets ranged from <10 percent of calories from fat to < 30 percent of calories from fat. The diet interventions used range from providing instructions at the start of the study only and expecting participants to follow the diet plan, to regular counseling sessions with dietitians, food diaries and cooking lessons, to actual feeding studies where participants were given much of their overall food intake. Some studies coached participants to cut calories while others, including those put on low-carbohydrate Atkins-style diets, were told to eat until they were full without consciously restricting calorie intake.

The authors sliced and diced the data before coming up with some conclusions. They analyzed results from 13 trials that examined weight maintenance as well as studies that didn’t include weight loss as a primary goal. In these studies, low-fat and high-fat diets led to a similar amount of weight loss. Low-fat diets were superior only when compared to the subjects’ normal diet. So, there was no clear frontrunner. The tiebreaker came from an analysis of 35 weight-loss trials, 29 of which were conducted using adults who were overweight, obese or had type II diabetes. Overall, there was no difference between low-fat and high-fat diet interventions. As expected, low-fat diets led to greater weight loss compared to groups following their usual diet. Yet the headlines that were plastered in large font on news websites and sprinkled over Facebook by high-fat diet advocates were pulled from a comparison between low-fat diets and high-fat diets that varied by more than 5 percent of calories. In this subset of the data, higher fat diets were the clear winner, leading to significantly greater weight loss after a year than low-fat diets. For added support, the authors cited two other meta-analyses that found low-fat diets do not improve weight loss results compared to high-fat diets.

The End of Low-Fat Diets?

Based on the results, the authors suggest low-fat diets shouldn’t be the go-to recommendation for weight loss. However, a closer look at the actual data reveals a few other interesting findings. First off, the results of this study are mainly applicable to overweight, obese and type II diabetics— the primary populations examined in these studies. We can’t take the authors’ conclusion that high-fat diets are better for weight loss than low-fat diets and apply it to the masses. What works for an obese adult or type II diabetic will not necessarily work for an active adult who wants to lose 10 or 15 pounds. This is especially true when considering that overweight and obese adults are more likely to have insulin resistance and, type II diabetics, by definition, have insulin resistance. Insulin resistance means your cells are not as receptive to the hormone insulin. During the initial stages of insulin resistance, your pancreas works harder by producing more insulin, a hormone that helps our bodies store extra calories, those that aren’t needed right away for energy, as glycogen (carbohydrate in muscle and liver) and fat. Though the temporary actions of insulin are definitely not the sole determinant of body fat, the combination of overproducing insulin plus a higher carbohydrate, higher calorie diet (more calories than necessary to maintain or lose weight) is a great recipe for gaining body fat.

How does this concept apply to this study? In these population groups— overweight, obese and type 2 diabetics, lowering the carbohydrate content of the diet may lead to greater weight loss initially (if they can follow the diet), which can help adherence. Research backs up this point by showing that weight loss over the first six months on a diet is the main predictor of both weight-loss success and sticking to a diet over the long term. People “fall off” the diet in studies just like they do in real life, especially if they don’t have regular nutrition coaching. In other words, if you are getting results, you are more likely to stick with the program. This makes a lot of sense, in weight loss and in life. However, both the results from this study and the concept of insulin resistance shouldn’t be used to throw out low-fat diets completely.

Focusing Only on High-Fat or Low-Carb is Pointless

Rating a weight-loss diet by macronutrient composition alone— low-fat, high-carbohydrate or high-fat, low-carbohydrate— isn’t very helpful for two reasons: 1) the type of fat and carbohydrate you eat makes a difference and 2) adherence and calories trump everything else. Put both of these together and you have a winning combination.

High-fat, low-carbohydrate diets have been used for several decades. These diets initially included plenty of foods high in saturated fat with little distinction made between bacon and salmon. Over time, these diets have evolved based on the latest scientific research and common sense. We now know that diets higher in polyunsaturated fats, the kind found in fatty fish and several types of plant-based oils including corn and sunflower oil, as opposed to diets high in saturated fat, lead to less belly fat.

When the tide turned to the low-fat craze of the 1990s, many people heard the word “fat” and ran, without paying attention to the quality of carbohydrates they were eating. The marketplace responded with supermarket store shelves overflowing with high sugar, highly refined yet low-fat foods. When this diet didn’t work and our collective waistline continued to expand, some blamed carbohydrates as the root cause of obesity. It wasn’t the carbohydrates but instead the type of carbohydrates we were eating. A diet primarily composed of high-fiber plant-based foods makes weight loss and weight maintenance a lot easier than highly refined, high sugar foods.

Putting it All Together: A Recipe for Weight-Loss Success

In addition to food quality, including the types of fats and carbohydrates you are consuming, overall calories matter. You must consume fewer calories than you burn each day to lose weight. Also, adherence matters. In this meta-analysis, higher fat diets fared better than low-fat diets. However, the results were hardly earth shattering. Participants on low-carbohydrate diets lost about 2.2 pounds more weight after one year versus those on a low-fat diet. A 2.2-pound difference in weight loss after one year on a diet isn’t very impressive, especially considering many of the subjects were overweight or obese to begin with. What’s more disappointing than the paltry 2.2-pound difference between the low-fat and high-fat diets after one year is the total average weight loss in the studies designed for weight loss— a mere 8.25 pounds after one year. Instead of declaring high-fat diets a clear winner over low-fat diets, we should be asking why people can’t stick with diets over a long period of time. Previous research has found any reduced calorie diet works as long as you stick with it. If we know it works, why aren’t we able to stay on a diet? This is the biggest research question of all and one that anyone attempting to lose weight should ask themselves.

If you want to lose weight, choose a lower calorie diet primarily based on high-quality foods or create your own plan that fits into your lifestyle and you can stick with it. Add permission to alter your plan as often as you need to based on changes in your lifestyle, motivation and results and you are more likely to be successful than if you fall into the trap of solely focusing on macronutrients.


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