One of the most common reasons people start a ketogenic diet or simply cut carbohydrates is to lose weight. But does the hard, scientific evidence say? Additionally, does a low-carb diet just get rid of the water weight- or does it shed body fat and maintain lean mass? In this piece we analyze if eating more fat really makes you less fat.
The Key Figures in Body Weight
Everyone is always talking about “losing weight”- but what are the exactly referring to? Human body weight refers to the amount of mass on your body. The bulk of this mass is from body fat, water, muscle, and bone. Being overweight means that you have extra body weight from fat, water, muscle, or bone.
Obesity means that someone has an excess amount of fat to the extent that it harms your health. Oftentimes, doctors, nurses, and other professionals will put your weight in terms of your height and gender in a figure called body mass index (BMI). According to the World Health Organization, a BMI from 25-30 usually indicates someone is overweight, BMI in the 30-35 range puts someone in the range of being obese and 35 and over morbidly obese. 
Medical and public health research suggests that body weight and BMI are useful indicators of health. According to the National Institutes of Health, being obese and morbidly obese is significantly associated with an increased risk of developing serious health issues such as certain cancers, heart disease, type 2 diabetes, high blood pressure, and kidney damage. [2, 3, 4] Maintaining a healthy weight is a critical way to prevent the onset of many of these health problems.
Recently, many people have begun to question the usefulness of BMI as a general indicator. A sizable amount of people who may be overweight or even obese may be classified as such even though they have a high amount of muscle. Conversely, people with a “healthy” or low BMI may have a high level of body fat and actually be at a greater risk for developing health problems. [5, 6]
Thus, many researchers and clinicians have noted that measuring body weight along with body fat percentage and waist circumference may be a better indicator of cardiovascular risk and overall health. [7, 8, 9, 10, 11]
Obesity and high body fat percentage are serious, widespread health concerns. It is one of the leading cause of preventable deaths in the world. In 2014, 600 million adults, or about 13% of the population, were obese while 42 million children under the age of five were obese. 
The United States has one of the highest rates of obesity in the world. The CDC estimated about 34.9% of adults and 17% of children are obese.  According to the WHO, an estimated 74.1 per cent of Americans were classified as overweight on 2007. 
Many experts agree that diet is one of the most important factors affecting body weight and body fat.  Thus, many have turned to research to assess the effectiveness of different diet plans. Can a high-fat diet help you lower fat? Below we check document the evidence.
Side By Side Comparison: How Does a Low-Carb Diet Stack Up?
In 2007, a team of eight research scientists compared the impact of the Atkins diet on body mass and body fat with three other diets in a 12-month randomized controlled trial. The team recruited 311 overweight and obese, premenopausal women with no history of diabetes or cardiovascular diseases. The women had an average age of 41 years, BMI of 32, and body fat percentage of 40. After taking baseline measurements, researchers distributed the subjects to one of four different groups.
The first group of 76 were asked to consume the Ornish Diet which had 10% or less of its calories from any type of fat. The next group of 79 followed the “LEARN Diet” which contained less than 10% of its calories from saturated fats and 55% to 60% of its calories from carbohydrates.
Additionally, the LEARN Diet emphasized behavioral modifications such as meditation and physical activity. The third group of 79 subjects ate “The Zone Diet”, which had a 40%, 30%, and 30% distribution of calories from carbohydrates, protein, and fats respectively. The final group of 77 were instructed to eat a low-carbohydrate Atkins diet.
Like the ketogenic diet, the subjects aimed to eat 20 grams of carbohydrates per day or less for a 2-3 month induction phase; then, they were asked to eat 50 grams of carbohydrates daily for the following 9-10 months. All participants were instructed to maintain a calorie deficit and utilize professional support to adjust to their diet and make sure that they stayed healthy. Additionally, the research team emphasized general health-promoting behaviors such as regular exercise and using nutritional supplements.
At the conclusion of the trial, all subjects that successfully completed their assigned diet experienced notable reductions in weight, body mass index, body fat percentage, and waist-to-hip ratio. However, those in the high-fat Atkins group had the greatest declines in each of these categories.
The average BMI in the Atkins group decreased by 1.65, by 0.92 in the LEARN group, by 0.77 in the Ornish group, and by 0.53 in the Zone group.  This means that the subjects who ate the Atkins diet decreased their BMI, on average, more than twice in the subjects from the high-carb diet Ornish group.
The results in body fat percentage lost was even more striking. The average body mass percentage decreased by 2.9% in the Atkins diet group. In contrast, it decreased by 1.5% in the Ornish diet group, by 1.3% in the Zone diet group, and 1.0% in the LEARN diet group.  This means that subjects in the Atkins diets decreased their average body fat percentage at least twice of any other group- including those eating the low-fat, high carbohydrate Ornish diet.
Finally, subjects in the Atkins diet group had the largest average decrease in their waist-hip ratio of 0.019.  The average decrease in the groups was 0.013 for Zone dieters, 0.012 for Ornish dieters, and 0.009 for the LEARN dieters. 
Due to the high-quality design and data of the study, it was published in the Journal of American Medicine, one of the most prestigious research journals in the world. The research team stated that “in this study of overweight and obese premenopausal women, those assigned to follow the Atkins diet had more weight loss and more favorable outcomes for metabolic effects at 1 year than women assigned to the Zone, Ornish, or LEARN diets.” 
Additionally, they remarked that “concerns about adverse metabolic effects of the Atkins diet were not substantiated within the 12-month study period.”  They acknowledged that more research needs to be done on the long-term effects on cardiovascular and metabolic health especially on men. However, their study supports the idea that a low-carbohydrate diet can help you lower body mass and body fat better than higher-carbohydrate alternatives.
Key Takeaways: In a 12 month period, a low-carbohydrate diet (<50 grams carbs/day) leads to a greater decrease in BMI, body weight, body fat percentage, and waist to hip ratio compared to other alternatives high-carbohydrate diets in a group of middle-aged women.
Recommendations: If you are interested in shedding body fat and losing weight, consider using a low-carbohydrate diet in conjunction with regular exercise and healthy food choices.
Low-Carb Diets with a Mediterranean Twist: More Effective?
Is it possible to fine-tune the ketogenic diet to yield stronger results? In 2008, a team of researchers from Spain examined how a Mediterranean-infused ketogenic diet impacts weight-loss. For their randomized, prospective study lasting 12 weeks, the team recruited 40 obese subjects (22 male and 19 female).
The average BMI of the subjects was 36.46 kg/m2 and their average age was 38.48 years. The subjects has no calorie restriction on their diet. However, they were instructed to eat no more than 30 grams of carbohydrates per day, consume at least 30 mL of virgin oil each day, and drink 200-400 mL of red wine daily.
Furthermore, they were encouraged to get their carbohydrates from green vegetables and salads and their protein from fish (except from large fish such as swordfish). The researchers designated their diet as the “Spanish Mediterranean Ketogenic Diet” (SKMD).
Thirty-one of the 40 subjects (78%) successfully completed the study. On average, the subjects had very large reductions in body mass and BMI. The average body mass decreased by 13.02% from 108.62 kg to 94.48 kg and the average BMI decreases from 36.46 kg/m2 to 31.76 kg/m2.
Additionally, while they didn’t quantitatively evaluate change in body fat percentage, they felt that body fat decreased because they “didn’t observe the flaccidity physical aspect that we have observed before with hypocaloric diets, and subjects had a physical aspect similar to a liposuction.” 
The authors of the study concluded that “the SKMD is safe, an effective way of losing weight, promoting non-atherogenic lipid profiles, lowering blood pressure and improving fasting blood glucose levels.”  However, they remarked on the importance of conducting studies with a bigger sample size and longer duration.
Key Takeaways: A low-carbohydrate diet using foods characteristic of the Mediterranean diet (fatty fish and greens) leads to significant weight-loss and reduction in BMI. A lot of this lost weight might be fat mass.
Recommendations: If you’re on or starting a ketogenic diet, consider incorporating Mediterranean foods such as olive oil (fat), fish (protein), and vegetables such as eggplant and green peppers.
Do Low-Carb Diets Work for Diverse Populations?
Recently, a group of ten research scientists sought to assess the effects of a low-carb diet on a diverse population. For their randomized, parallel-group trial lasting 12 months, they recruited obese 148 men and women and assigned them to one of two groups.
The first group of 75 consumed a low-carbohydrate diet with less than 40 grams of carbohydrates per day. The second group of 73 consumed a low-fat diet with less than 30% of calories from fat and less than 7% of calories from saturated fat. Both groups regularly received nutritional counseling periodically throughout the study meeting with each participant meeting with a dietitian for a total of 10 sessions
The participants had an age range of 22 to 75 years with an average age of 46.8 years. They had a BMI range of 30 to 45 kg/m2. About 88% of the participants were female and 51% were of African origin; thus, it was considerably more diverse than the prior study. They were also free of cardiovascular and renal complications including type 2 diabetes, cardiovascular diseases, and kidney disease as well as significant weight-loss in the past six months.
At the end of the twelve months, 60 participants (about 82%) in the low-fat group and 59 participants (about 79%) in the low-carbohydrate group successfully completed the trial. The decrease in body weight was substantially greater in the low-carbohydrate diet group which lost four times as much weight as the low-fat group (1.1 kg vs. 4.4 kg). 
Furthermore, the participants who ate the low-carbohydrate diet lost an average of 0.8% body fat while those that ate the low-fat diet gained an average of 0.7% body fat.  This suggests that a higher fat diet may improve may lead to more favorable changes in body composition. Subjects in both groups notably reduced their waist circumference.  However, the reduction was greater for the low-carbohydrate group. 
Because of the data, the research team stated that “the low-carbohydrate diet was more effective for weight loss and cardiovascular risk factor reduction than the low-fat diet. Restricting carbohydrates may be an option for persons seeking to lose weight and reduce cardiovascular risk factors.”  They also noted that “no serious adverse events were reported during the course of the study.”  Thus, the ketogenic diet might be a both a safe and effective weight-loss plan for you.
Key Takeaways: In a diverse population of obese, middle-aged women, a low-carbohydrate diet led to greater reductions in body fat percentage, body mass, and waist circumference over the course of 12 months when compared to a low-fat diet.
Recommendations: If you are looking to lower body fat in addition to lose weight, a low-carbohydrate, ketogenic diet is a stronger choice than a higher carbohydrate alternative.
An Overview of the Research
In 2014, a group of three Brazilian researchers assessed the available literature on low-carbohydrate diets in a meta-analysis. They specifically looked at trials that compared a very-low carbohydrate ketogenic diet (VLCKD) that contained no more than 50 grams of carbohydrates per day against a conventional, low-fat diet with less than 30% of calories from fat. Ultimately, they included 13 studies that lasted 12 months or more and collectively contained 1577 subjects with 787 randomized to a low-fat diet group and 790 to a VLCKD group.
When examining the studies, the researchers noted that, on average, the participants in the VLCKD groups lost about 2 lbs. more of bodyweight compared to the low-fat diet groups.  This difference was statistically significant and described as “moderate”. The researchers also noted greater improvements in triglycerides, blood pressure, and HDL cholesterol in the VLCKD group compared to the low-fat diet group.
However, they did not assess other key indicators of health including body fat and waist circumference. Because of these findings, the researchers stated that “individuals assigned to a VLCKD achieve a greater weight loss than those assigned to a LFD in the long-term; hence, a VLCKD may be an alternative tool against obesity.” 
These findings are in line with another meta-analysis on 13 randomized controlled trials lasting at least six months comparing low-fat and low-carbohydrate diets. They noted that at six months, subjects who consumed less than 60 grams of carbohydrates per day had an average greater weight-loss of 8.8 lbs. compared to subjects on low-fat diets.  At one year, the difference had fallen to only 2.3 lbs. 
However, the researchers noted that it was still substantial and noted that “Evidence from this systematic review demonstrates that low-carbohydrate/high-protein diets are more effective at 6 months and are as effective, if not more, as low-fat diets in reducing weight and cardiovascular disease risk up to 1 year.”  They emphasized, however, that more research needs to be done to evaluate the long-term effects of the ketogenic diet on weight-loss.
Key Takeaways: Two large-scale meta-analysis indicate that people who consume a low-carb diet (<50 g carb/day) lose a slightly larger amount of weight compared to people eating a low-fat diet over 12-month span. Neither meta-analysis assessed the loss in body fat percentage within each diet and which other dietary of exercise interventions promoted weight-loss when coupled with the ketogenic diet.
Recommendations: Most of the evidence suggests that a low-carbohydrate diet is a moderately effective alternative to a low-fat diet in reducing body weight over a year span. Very little evidence suggests that it a high-fat diet is “worse” for weight-loss than a low-fat diet.
Are Low-Carb Diets Always Effective?
Not every study supports the notion that a low-carb diet is more effective for weight-loss than other diets. One study lasting 12 months on 132 obese subjects compared a ketogenic diet (<30 g of carbs per day) against a diet with a 500 kilo-calorie deficit.
The authors noted that “weight loss was similar between groups” . However, they emphasized that “effects on atherogenic dyslipidemia (cholesterol) and glycemic control were still more favorable with a low-carbohydrate diet after adjustment for differences in weight loss.”  Another study noted that the low-carb diet promoted greater weight-loss than a standard low-fat diet for the first six months. However, these differences were small after one year. 
Another study lasting 6 months noted that subjects on the ketogenic diet had greater weight-loss when compared to a low-fat group. However, they emphasized that “future studies evaluating long-term cardiovascular outcomes are needed.” 
It is important to note that these studies often showed some favorable effects of the ketogenic diet (such as reduced triglycerides) compared to low fat diets. Additionally, none of them measured body fat or waist circumference.
Should You Restrict Calories or Carbs for Weight Loss? What Matters Most?
The data on low carb diets clearly and consistently support how effective cutting the carbs can be for weight loss. However, what these studies don’t tell us is WHY carb restriction works so well.
To figure out the mechanism behind the results, we must look at studies that control as many variables as possible to see if restricting carbs or calories is the key to weight loss.
Fortunately, Drs. Kevin Hall and Juen Guo had the same burning question. In 2017, they analyzed the data and published a meta-analysis of controlled feeding studies that compared diets of equal calorie and protein content with variations in carbohydrate and fat content.  By filtering out the diet data in this way, the researchers could finally find out whether restricting carbs or limiting calories is more important when it comes to weight loss.
After investigating 20 controlled feeding studies, Hall and Guo found that both low-carb and high-carb diets had similar effects on body fatness and energy expenditure. The results of this meta-analysis provide us with high-quality evidence that supports the widely-believed theory that calories matter much more than the fat or carbohydrate content of the diet when it comes to weight loss. 
Thus, instead of focusing on switching out carbs for fat or vice versa, we should focus on sticking to a diet that naturally decreases our calorie intake.
This meta-analysis also provides us with an explanation for why keto and low-carb diets have not always been found to confer better weight loss than low-fat diets. When protein and calories are controlled, changes in weight loss results remain relatively equal. This not only supports the theory that calorie deficits are the key to weight loss, but it also provides evidence against the hypothesis that carbs and insulin are the cause of obesity. 
In short, this meta-analysis of controlled feeding trials shows us that the key factor for weight loss is maintaining a calorie deficit.  The concept is simple enough, but it is not easy for many of us to execute.
Fortunately, the research literature also provides us with plenty of evidence supporting the effectiveness of one diet in particular that can make weight loss both simple and easy for many people.
What Makes the Keto Diet So Effective for Weight Loss?
Although the controlled feeding studies show no magical difference between low-carb and low-fat diets when it comes to weight loss, these studies don’t accurately reflect our food environment.
Our caloric expenditure and intake are not being rigidly tracked by scientists, and our meals aren’t being formulated for a specific macronutrient and calorie content. In the real world, we are inundated with palate-pleasing temptations that are dangerously convenient to consume in copious amounts.
To lose weight and keep it off, we must fight against this obesogenic (fat-gain promoting) environment and our own cravings and hunger pangs to maintain a calorie deficit.  Simple in concept, but not easy to implement, as demonstrated by the rising obesity rates in westernized societies. 
Fortunately, it is possible to make weight loss easier to accomplish. According to the research that mimics real-world scenarios (like many of the studies we looked at earlier), the low-carb diet works incredibly well by making weight loss more feasible and sustainable.
However, if carbs aren’t the culprit — as we found out in the previous section — why are low carb diets so effective?
Although many factors contribute to weight loss, here are the two principles that explain why cutting carbs works so well:
- By restricting carbs, you naturally increase your consumption of high-fat, protein-dense, and fiber-rich foods. These foods boost satiety levels in the short- and long-term, which causes you to eat fewer calories than before. 
- By restricting carbs, you are eliminating virtually all calorically-dense processed foods from your diet. These foods are typically so palatable that they cause us to consume too many calories and gain fat. 
Put in another way, the low carb diet primarily consists of highly-satiating foods like meat, fish, and low-carb vegetables while cutting out all carb-ridden, highly-palatable foods. By eating in this way, most people experience a significant amount of fat loss because they tend to eat fewer calories than they did previously without realizing it.
Furthermore, if you restrict carbs to the point of provoking nutritional ketosis (i.e., by following a keto diet), you will also experience the appetite-suppressing effects of ketones — an alternative fuel source that will help keep your energy levels high and calorie consumption low so that you can lose more fat without missing a step.
Putting It All Together — Key Takeaways from the Keto & Low-Carb Weight Loss Research
The bulk of research indicates that the ketogenic diet is more effective than conventional diets in helping you lose weight and shed body fat. A handful of studies suggest that low-carb diets are equal to low-fat diets in helping you lose weight in the long term. Based on a broad picture of the literature, we can reasonably assert that:
- Weight loss caused by low-carb diets isn’t just because of a loss of “water weight”. In research studies that measured change in body fat, subjects eating low-carb diets had a greater loss in body fat than those eating low-fat diets. Additionally, keto diets lead to a greater reduction in waist circumference, a critical indicator of harmful stomach fat.
- A ketogenic diet accompanied by regular physical exercise and smart diet choices, such as eating more low-carbohydrate vegetables and fatty fish, increase its effectiveness in shedding excess weight and fat.
- Virtually no studies or meta-analyses of the literature suggest that low-carb diets are less effective in helping you lose weight than low-fat diets. The most critical studies of low-carb diets say that it as “at least” effective as low-fat diets, and many suggest that it is more effective in helping you lose weight.
- Being in a calorie deficit is the key to weight loss. Low carb diets are effective not because carbs are fattening, but because cutting carbs increases the satiety of the diet and reduces calorie consumption.
- Consistency is important. Most of the studies that yielded good results did so because subjects kept track of their calorie intake and made healthy lifestyle choices.
- Combine this with the long-term health benefits of the ketogenic diet, and it becomes a fantastic blend of both short- and long-term results.
How do you know if a strict ketogenic diet or simply cutting some carbs is the right dietary approach for you? First, consult with your doctor and a dietitian to see if it is a suitable plan for you based on your medical history. Then, use the guides, articles, and recipes on Ruled.me to create a well-organized weight-loss plan. Remember to make healthy diet choices, such as eating fatty fish and high fiber vegetables, and supplement with exercise to get the best results.
If you’d like to find more practical suggestions on what you can do to lose weight using the keto diet, check out the articles below:
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*Written in collaboration with Neel Duggal