Researchers studied 30 adults with obesity who followed a modified ketogenic diet (a very low-carb eating plan) for just two weeks. The participants lost about 5% of their body weight while keeping their muscle mass stable. Blood tests showed interesting changes in special proteins that control metabolism and in the different types of cholesterol in their blood. The study suggests that even a short period of eating this way can trigger quick changes in how the body processes fat and manages cholesterol, though the long-term effects remain unclear.

The Quick Take

  • What they studied: Whether a modified ketogenic diet (a diet very low in carbohydrates) for two weeks would change body weight, muscle mass, and specific blood markers related to metabolism and cholesterol in people with obesity.
  • Who participated: 30 adults with obesity (BMI of 28 or higher) who were otherwise metabolically healthy. All participants followed the same diet plan for two weeks and had their measurements taken before and after.
  • Key finding: After two weeks, participants lost about 4.8% of their body weight (roughly 4.5 pounds on average) and 4.7% of their BMI, while keeping their muscle mass essentially unchanged. Blood tests showed a significant increase in a protein called GDF15 and a dramatic 52% decrease in another protein called FGF21. The types of cholesterol particles in their blood also shifted toward larger, potentially healthier forms.
  • What it means for you: A short-term ketogenic diet may help people lose fat quickly without losing muscle, and it appears to trigger rapid changes in metabolism-regulating proteins and cholesterol particle types. However, this was only a two-week study in a small group, so we don’t yet know if these changes are beneficial long-term or if they continue beyond two weeks.

The Research Details

This study used a simple but effective design called a self-controlled pre-post study. Thirty adults with obesity participated in a two-week modified ketogenic diet intervention. Researchers measured each person’s body composition (how much fat versus muscle they had), blood levels of two special proteins (GDF15 and FGF21), and the different types of cholesterol particles in their blood before the diet started and immediately after it ended.

The modified ketogenic diet is a very low-carbohydrate eating plan that shifts the body’s energy source from carbohydrates to fats. All participants followed the same dietary guidelines for the full two weeks, and researchers carefully tracked their measurements at both time points to see what changed.

This type of design is useful for detecting rapid changes because each person serves as their own comparison point, eliminating differences between individuals. However, it doesn’t include a control group (people who didn’t follow the diet), so we can’t be completely certain the diet caused all the changes observed.

Understanding how the ketogenic diet affects metabolism is important because obesity is a major health problem worldwide. This study specifically looked at two proteins—GDF15 and FGF21—that researchers believe play key roles in how the body loses weight and manages cholesterol. By measuring these proteins alongside traditional cholesterol measurements, the study provides a more complete picture of what happens in the body during a ketogenic diet. The focus on cholesterol particle types (not just total cholesterol) is also important because different sizes of cholesterol particles may have different effects on heart health.

Strengths of this study include careful measurement of body composition and blood markers using standardized methods, and the fact that all participants were metabolically healthy at the start (reducing confounding factors). The study was registered before it began, which is a good sign of scientific integrity. However, the study has important limitations: only 30 people participated (a relatively small group), there was no control group for comparison, and the intervention lasted only two weeks. The participants were likely volunteers who were motivated to follow the diet, which may not represent the general population. Additionally, we don’t know if the changes observed would continue beyond two weeks or if they would lead to better health outcomes.

What the Results Show

After two weeks on the modified ketogenic diet, participants experienced significant weight loss. On average, they lost 4.8% of their body weight (about 4.5 pounds for someone weighing 200 pounds) and reduced their BMI by 4.7%. Importantly, their lean muscle mass remained essentially stable, with changes of less than 3%, meaning the weight loss came primarily from fat rather than muscle.

Blood tests revealed striking changes in two metabolism-regulating proteins. GDF15 levels increased by 5.76%, which was statistically significant. FGF21 levels dropped dramatically by 51.91%—this was a very large and highly significant change. These proteins are thought to play important roles in how the body burns fat and manages energy.

The study also found important changes in cholesterol particle types. The ratio of apolipoprotein B to apolipoprotein A1 increased significantly, as did the LDL-cholesterol to HDL-cholesterol ratio. However, the distribution of HDL-cholesterol particles shifted toward larger, potentially healthier forms. Specifically, the larger HDL particles (H1FC and H2FC) increased, while smaller HDL particles (H3FC and H4FC) decreased. The H2FC particle type showed the most dramatic increase.

Beyond the main findings, the study documented that all measured changes occurred within just two weeks, suggesting the body responds very quickly to the ketogenic diet. The stability of muscle mass across all measured types (skeletal muscle mass, skeletal lean mass, and fat-free mass) indicates that the diet preserved muscle tissue despite the rapid weight loss. The changes in cholesterol particle distribution are noteworthy because they suggest the diet may be improving the quality of cholesterol in the blood, not just the quantity. The simultaneous increase in GDF15 and decrease in FGF21 represents an interesting metabolic shift that researchers believe may be important for understanding how ketogenic diets work.

This study adds to existing research showing that ketogenic diets can produce rapid weight loss. Previous studies have documented similar fat loss rates with low-carb diets. However, this research is notable for its detailed examination of specific metabolic proteins (GDF15 and FGF21) and cholesterol particle types, which goes beyond what many earlier studies measured. The finding that muscle mass remained stable aligns with some previous research suggesting that ketogenic diets can preserve muscle during weight loss, though this isn’t universal across all studies. The dramatic decrease in FGF21 is particularly interesting because some previous research suggested this protein might increase on ketogenic diets, so this finding may help clarify conflicting earlier results.

This study has several important limitations that readers should understand. First, the sample size was small (only 30 people), which means the results may not apply to larger, more diverse populations. Second, there was no control group—we don’t know what would have happened if these same people had eaten their normal diet for two weeks, so we can’t be completely certain the diet caused all the observed changes. Third, the study lasted only two weeks, so we have no information about what happens after that point. Do the changes continue? Do they reverse? We don’t know. Fourth, all participants were volunteers who chose to follow the diet, and they were metabolically healthy at the start, which may mean they’re not representative of all people with obesity. Finally, the study didn’t measure actual health outcomes like heart disease risk or diabetes development—it only measured blood markers and body composition, so we can’t conclude whether these changes actually improve health.

The Bottom Line

Based on this research, a modified ketogenic diet appears to produce rapid fat loss while preserving muscle mass in the short term (at least two weeks). The changes in metabolism-regulating proteins and cholesterol particle types suggest the diet triggers significant metabolic shifts. However, confidence in long-term recommendations is low because this was a short-term study. If you’re considering a ketogenic diet, discuss it with your doctor first, especially if you have any existing health conditions, take medications, or have a family history of heart disease. The diet may be worth trying as a short-term weight loss tool, but we need longer studies to understand whether the metabolic changes observed are beneficial over months or years.

This research is most relevant to adults with obesity who are looking for effective weight loss strategies and are interested in understanding how their body responds to dietary changes. It may be particularly interesting to people concerned about preserving muscle mass during weight loss. However, this study should NOT be used to make decisions for people with diabetes, heart disease, kidney disease, or those taking certain medications, as the ketogenic diet may not be appropriate for these groups. Pregnant or breastfeeding women should also avoid making major dietary changes without medical guidance. The study results apply specifically to relatively short-term use (two weeks), so people interested in long-term ketogenic diets should seek additional research and medical advice.

Based on this study, significant changes appear within two weeks: weight loss of about 5% and major shifts in blood markers. However, the study didn’t track what happens after two weeks, so we don’t know if benefits continue, plateau, or reverse. Most people would likely see noticeable weight loss within the first two weeks, but realistic expectations for sustained benefits beyond that point require longer-term research. Individual results will vary based on starting weight, metabolism, and how strictly the diet is followed.

Want to Apply This Research?

  • Track weekly body weight and waist circumference measurements, along with how much muscle mass you’re maintaining (if you have access to body composition scales). Record these measurements every 3-4 days to see the rapid changes this diet appears to produce. Also note energy levels and muscle strength to monitor whether muscle is being preserved.
  • If trying a ketogenic diet, use the app to log your daily carbohydrate intake (aiming for very low amounts), track protein consumption (to help preserve muscle), and monitor fat intake. Set a two-week goal to test whether this approach works for you, then reassess with your doctor before continuing longer-term.
  • Create a dashboard showing weekly weight trends, body composition changes, and subjective measures like energy level and hunger. Set reminders for weekly weigh-ins and measurements. After two weeks, review your results and discuss them with your healthcare provider before deciding whether to continue. If continuing, track whether the rapid initial changes slow down or stabilize, as this study only measured the first two weeks.

This study examined a two-week ketogenic diet in 30 metabolically healthy adults with obesity. The findings suggest rapid changes in body weight, muscle preservation, and blood markers, but this was a short-term study without a control group. These results should not be used to diagnose, treat, or prevent any disease. Before starting a ketogenic diet or making significant dietary changes, consult with your doctor or registered dietitian, especially if you have diabetes, heart disease, kidney disease, are pregnant or breastfeeding, or take medications that may interact with dietary changes. Individual results vary, and what works for one person may not work for another. This research provides interesting preliminary findings but should not replace personalized medical advice.