Back to Studies

Study analysis · iScience · 2024

This diet lost people 14% of their belly fat—without cutting calories or losing muscle.

People who ate mostly fat and very few carbs for three months lost belly fat, kept their muscles, and felt way more energetic and happier.

Reading level
Low certainty
Level 2b · Individual cohort studyAssociation, not causationNo causal claims

Overview

What the study found

The study in plain English — the bottom line, every takeaway we extracted, and what to do with them.

In simple terms

This study watched what happened when people ate a low-carb diet for a few weeks or months, and noticed they lost weight and felt better. But since people chose for themselves whether to eat that diet, we can't be sure the diet was the reason they felt better — maybe they just started walking more or sleeping better.

What’s the bottom line?

People who ate mostly fat and very few carbs for three months lost belly fat, kept their muscles, felt more energetic, and felt less tired and happier.

How strong is this study?

The researchers did a good job measuring things like body fat and energy levels carefully, and made sure people were really in ketosis. But because they didn't randomly assign people to diets, and everyone knew what they were eating, we can't trust that the diet alone caused all the changes — it's like noticing your phone battery lasts longer after you turn off apps, but maybe you just stopped using your phone as much.

Reporting

40 / 100

  • COI disclosure+40/40
  • Data availabilitydata not shared
  • Code availabilitycode not shared
Methodology

40 / 100

  • Randomizationnot randomized
  • Blindingnot blinded
  • Control group+15/15
  • Sample size (n=81)+6.7/20
  • Follow-up+10/10
Publication

100 / 100

Statistical

46 / 100

  • P-values+15/15
  • Effect sizeno effect size reported
  • Confidence intervalsno confidence intervals
  • Pre-registration+15/15

Each component is scored out of 100 and then capped by the study design — a case series cannot reach the ceiling a randomised trial can, however well it is reported.

Where it sits

RCT reviews

Max 100

Randomized Trials

Max 90

Reviews of Cohort Studies

Max 85

Cohort Studies

Max 72

Reviews of Case-Control Studies

Max 63

Case-Control Studies

Max 58

Cross-Sectional & Case Series

Max 50

Expert Opinion

Max 5
StrongerWeaker
Cohort Studies
Level 2b
53

53 / 100

Probability of being correct

Groups of people are followed over time to see who develops an outcome. Strong for identifying risk factors and associations, but cannot prove causation as firmly as RCTs.

This design cannot establish causation — the findings describe an association, not a cause. This is a prospective pre-post interventional study without randomization or blinding. While it has a control group for counseling bias, participants chose their diet group, introducing selection bias. Changes over time cannot be definitively attributed to the ketogenic diet alone, as other factors (e.g., increased awareness, lifestyle changes) may contribute.

No Conflicts

No conflicts of interest identified

No conflicts of interest or funding disclosures were reported in the study text. The study appears independently conducted with no indication of industry influence.

The study lacks any declared funding sources or conflict of interest statement. While the results appear methodologically sound, the absence of transparency regarding funding raises a minor transparency concern, though no evidence of bias or industry influence is present.

Key takeaways

  1. 01

    Lost 14.3% body fat, 14.7% belly fat, gained 35.6% more energy, improved mental health by 21.3%, reduced fatigue by 17.9%, raised good cholesterol (HDL) by 5.7%, and lowered blood sugar by 6.3%.

  2. 02

    Yes—losing belly fat and feeling more energetic and less tired can make daily life much easier, especially for people who are overweight and often feel drained.

Surprising findings

  • Weight loss occurred without calorie restriction.Everyone assumes you must eat fewer calories to lose weight. This study showed fat loss happened purely by changing macronutrient ratios—suggesting insulin and metabolic signaling may be more important than 'calories in, calories out.'
  • Fatigue improved most in those who were most fatigued at baseline.It’s counterintuitive that a restrictive diet would help people with chronic fatigue—but the study found the more tired you were at the start, the more you improved (r=0.69). This suggests keto may target underlying metabolic inflammation.
  • No adverse metabolic changes occurred despite high fat intake.For decades, high-fat diets were blamed for heart disease. This study found no rise in LDL, triglycerides, or inflammatory markers—challenging the foundational assumption behind low-fat dietary guidelines.

Practical takeaways

Try a 3-month eucaloric ketogenic diet (<10% carbs, ~60% fat) if you're overweight and tired—track ketones with a blood meter to ensure you're in ketosis.

This study had intensive nutritional counseling and objective monitoring—most people won't have that support, and results may vary without it.

medium confidence

If you're struggling with low energy or brain fog, reducing carbs—even without cutting calories—might improve your vitality and mental clarity.

Results were strongest in overweight participants; healthy normal-weight people saw smaller benefits.

medium confidence

Use keto as a metabolic reset—not a lifelong diet. Consider cycling in and out to maintain benefits without burnout.

Long-term effects beyond 3 months are unknown. Maintenance strategies weren't studied.

low confidence

Why this study matters

Fat Loss Without Muscle Loss

Participants lost 14.3% of their total fat mass and 14.7% of their visceral (belly) fat over three months—while muscle and bone mass remained completely unchanged. This was achieved on an eucaloric diet (no calorie reduction), meaning weight loss came purely from metabolic shift, not hunger.

Most diets force you to choose between losing fat or losing muscle—this study shows you can lose stubborn belly fat without sacrificing strength or metabolism, which is huge for long-term health and body image.

Energy & Mental Health Surge

Participants reported a 35.6% increase in vitality and a 21.3% improvement in mental health—measured by validated SF-36 and WHOQOL-BREF questionnaires. Fatigue dropped by 17.9%, especially in those who started with high fatigue levels.

This isn't just about weight loss—it's about feeling less drained, less anxious, and more alive. People don't just want to lose weight; they want to stop feeling exhausted all the time.

Cholesterol Didn't Go Up—It Got Better

Despite eating high fat, HDL ('good' cholesterol) increased by 5.7%, while LDL, triglycerides, and ApoB/A1 ratios stayed flat. No adverse lipid changes were observed—contrary to decades of dietary fear-mongering.

The myth that 'fat = bad cholesterol' is still everywhere. This study directly challenges it with hard numbers from a controlled human trial.

Blood Sugar Improved—Without Medication

HbA1c dropped by 6.3% and fasting glucose by 6.5% over three months—without any diabetes drugs. This suggests keto can improve metabolic health even in non-diabetic overweight adults.

People with prediabetes or insulin resistance are desperate for non-pharmaceutical solutions. This shows diet alone can reverse early metabolic damage.

Want the whole report?

Detailed mode opens the full scientific breakdown — every score component, the methodology, conflicts of interest, the evidence analysis behind each claim, and the raw study data.

Standing

The people behind it

The researchers who wrote the study this analysis is built on.

Authored by

8 researchers

If this is your work, this is how we attribute it on Fit Body Science. Simon Hirschberger is listed as the lead author.