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The information cacophony associated with diets never seems to let up. Today, we face a dizzying array of diets with differing messages that have been broadcasted in books, on social media, during podcasts and in gym changing rooms. These include, but are certainly not limited to, various guises of low‐carbohydrate diets (yes, the Atkins diet is still floating around). But do you really have to adopt a low-carb diet if you’re hoping to lose weight?
Few things are more vilified than carbs. Seemingly every day, a new health expert is bashing on this macronutrient and its connection to weight gain. And with about half of all American adults reporting that they’d like to achieve a healthier weight from their frame, it’s easy for people to latch onto the “carbs are bad, bacon is good” mindset. Driving up blood sugar, promoting insulin resistance, consuming calories with little nutritional value, and stimulation of the brain reward areas leading to overeating are all ways that carbs have been blamed for contributing to weight gain.
Low‐carbohydrate diets are a broad category that includes a wide range of restrictions with varying levels of protein and fat used as replacement calories. They can be implemented in different ways, but they all typically call for the restriction of grains (both refined and whole), legumes, fruits and starchy vegetables to get your carb intake below a certain level. A ketogenic low-carb diet, for example, may allow for only 50 grams of carbohydrates – not much more than what’s in a couple of slices of bread – while other approaches are more forgiving, suggesting you eat no more than 200 grams daily.
But very few people start these diets by examining the scientific evidence behind the claims. Low‐carb diets continue to be widely promoted, marketed and commercialized as being the most effective for immediate and lasting weight loss, not to mention as being much healthier than diets higher in carbs. But there’s a catch: This perspective isn’t necessarily accurate.
In fact, we can definitively reject the claim that carbohydrate restriction is an absolute requirement for body fat loss. Here’s why your favorite carbs need not be sent packing when trying to eat for a slimmer waistline.
In defense of carbs
What might be the most comprehensive study comparing body weight reduction and heart disease risk factors associated with low-carbohydrate weight‐reducing diets with diets that allow for a more liberal intake of carbs provides some good news for people who want to achieve a healthier weight but still enjoy carbohydrates.
The expansive research review published in Cochrane Reviews included 61 randomized controlled trials that randomized a total of 6925 male and female participants who were overweight or living with obesity (average weight 210 pounds), without or with type 2 diabetes and without or with cardiovascular conditions, to either low-carbohydrate (less than 45% of total daily calories) or balanced-carbohydrate weight-reducing diets (45% to 65% of total daily calories).
Nearly half of the trials included were conducted in the United States. The most common lower-carb diets used in studies provided 20 to 35% of energy from carbs and 20% or more of calories from protein. But some trials included in the investigation provided no more than 10% of energy from carbs and were very low in the macronutrient. For a trial to be included in this review, the weight-reducing phase had to be 2 weeks or longer, with the main goal to elicit weight loss in participants. The longest dieting phase was two years, but most trials lasted 6 months or less. This speaks to the challenges such as the financial costs of conducting long-term nutrition investigations.
The results of a low-carb diet
After crunching the numbers, the study authors found little evidence that there was a clinically significant weight loss difference between lower- and higher-carbohydrate diets over the short- and long-term in people with and without type 2 diabetes.
In the short term, the average difference in weight loss was about 2.2 pounds. In the long term, the average difference was less than 2.2 pounds.
The low-carb diets came out slightly ahead in terms of weight loss in both of these timeframes, some of which could be attributed to body water loss that occurs during dietary carb restriction due to glycogen depletion and ketone production. There were also no notable differences found in health measures including blood pressure, LDL cholesterol and HbA1c, a measure of blood sugar levels over 2 to 3 months.
It’s worth noting that the degree of body weight lost varied greatly with both types of diets across the trials from less than 2.2 pounds in some studies and up to about 26 pounds in others. The effects of low-carbohydrate diets compared to balanced-carbohydrate diets beyond two years is unknown, as reliable data wasn’t available to the investigators.
Since most low-carb diets naturally include higher levels of protein, these results challenge the belief that simply ramping up protein intake is guaranteed to help you shed more weight than eating more modest amounts of protein and higher amounts of carbs.
You don’t have to go low-carb to achieve a healthy weight
Let’s look at more evidence that carbs need not be off the menu if you want to scale down.
In this well-designed study published in JAMA, 609 adults aged 18 to 50 years without diabetes and with a body mass index that placed them in the overweight or obese category were randomized to follow a healthy low-fat diet (48% carbs, 29% fat, 21% protein) or healthy low-carb diet (30% carbs, 45% fat, 23% protein) for one year. The participants received 22 diet-specific education sessions administered over 12 months so they had a better grasp on their caloric needs and what healthy foods fit into their diet. This was important to assure that differences in overall diet quality would not be a contributing factor to the weight loss results.
In the end, weight loss at 12 months was 11.7 pounds for the higher-fat group compared to 13.2 pounds for the higher-carb group. So, there was hardly enough difference to declare one diet the winner in the battle of the bulge. And it’s worth noting the collection of scientists from the Stanford University School of Medicine found that neither genotype pattern nor baseline insulin secretion was associated with how the diets impacted weight loss.
The takeaway? As long as people eat a diet composed mostly of healthy foods within their allotted calories, the macro balance may not matter as much as we’re led to believe.
These results are in line with this meta-analysis also published in JAMA which found that both low-carb and low-fat diets can result in substantial weight loss, but differences between various diets including Zone and Atkins are minimal. And both low-carb and low-fat appear to be effective at helping people overcome metabolic syndrome, a cluster of conditions including high blood pressure and cholesterol, elevated blood sugar and excess body fat that can place people at risk for diabetes and heart disease.
Additionally, a controlled feeding study in the journal Cell Metabolism which confined subjects to a metabolic ward where they were provided with calorie-restricted diets that were lower in fat (only 8% of total calories) or lower in carbs (29% of total calories) found that, calorie for calorie, restriction of dietary fat led to greater body fat loss than restriction of carbohydrate in overweight adults. This occurred even though only the carbohydrate-restricted diet led to decreased insulin secretion and a substantial sustained increase in net fat oxidation compared to a baseline diet.
This tosses some shade at the claims that carb restriction offers a metabolic advantage for enhancing body fat loss. It should be mentioned that the study didn’t address whether it would be easier for people to adhere to a reduced-fat or a reduced-carbohydrate diet under free-living conditions instead of within the confines of the laboratory where food intake was strictly enforced. In the real world, diets only work if someone can stick with them.
Lastly, a prospective cohort study and meta-analysis that combined 25 years of follow-up of the Atherosclerosis Risk in Community (ARIC) data (USA) and seven other international cohort studies assessed the association between carbohydrate intake and mortality. Findings indicated that both high- and low-carbohydrate diets increased mortality, with the lowest risk observed among those who consumed a diet containing 50% to 55% carbohydrates.
It’s reasonable to assume that the high-carb diets resulted in a greater intake of refined carbohydrates and sugars. The low‐carbohydrate dietary patterns that favored animal fat and animal-based protein sources were associated with higher mortality, while those that favored plant‐based foods were associated with lower mortality.
The take-home message about low-carb eating
What do all of these results suggest? Well, perhaps it’s time to stop fussing so much over how many carbs, protein and fat we’re eating when it comes to achieving a healthy body composition.
Certainly, some form of dietary modification remains a key for most people to achieve a healthy weight. Few can maintain not-so-healthy habits and expect to have good results when stepping on the scale. But we have plenty of evidence to show that no one dietary strategy is consistently superior to others.
Evidence from decades of research demonstrates that adherence to diets where an energy deficit is achieved is a primary driver of weight-loss success, regardless of the macronutrient composition. This is a basic law of thermodynamics – weight loss occurs when the amount of calories consumed is less than the amount of calories expended.
And it’s very plausible that previously observed differences in weight loss and body fat change during diet interventions were primarily due to differences in overall calorie intake rather than any metabolic advantage of a certain macro distribution.
Weight loss may come faster on a low-carb diet, but as the weeks pass, the differences become less apparent. Yet when it comes to weight maintenance over the long-term, there is a chance that a certain macro distribution – such as lower-carb and higher protein – works best. Whether this is the case or not remains largely unproven and mostly speculation, though.
Instead of slamming one macronutrient or another, there needs to be a greater emphasis placed on total dietary patterns by guiding people towards choosing healthier foods (i.e. whole grains instead of refined grains, fish versus bacon and olive oil instead of butter) in amounts that keep calorie intake in line with what is required to achieve better health.
There’s more than one way to eat for your desired weight, since there is no “one‐size‐fits‐all” diet. Different diets work for different people, based on preferences and ease of adherence. Some people do better on low-carb, high-fat keto diets while others thrive on plant-based higher-carb diets; that’s just the reality. Remember, it’s essential that any diet you follow doesn’t leave you with a feeling of dread every time you open the fridge.
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