# Effects of a Very Low-Carbohydrate High-Fat Diet and High-Intensity Interval Training on Visceral Fat Deposition and Cardiorespiratory Fitness in Overfat Individuals: A Randomized Controlled Clinical Trial

PMID: 34993222
Journal: Frontiers in nutrition
Published: 2021
Authors: Cipryan L, Dostal T, Litschmannova M, Hofmann P, Maffetone PB, Laursen PB

## Question

What are the separate and combined effects of a very-low-carbohydrate high-fat diet and walking-based HIIT on visceral fat, body composition, and cardiorespiratory fitness in overfat adults?

## Summary

In adults with overweight or obesity, a very-low-carbohydrate high-fat diet reduced visceral fat and other body-fat measures over 12 weeks, while HIIT improved exercise time but did not independently reduce visceral fat. Combining VLCHF with HIIT improved exercise capacity but did not add clear visceral-fat benefit beyond the diet condition.

## Population

- Ninety-one nonsmoking adults aged 20-59 years with BMI 25-40, low physical activity, no regular sports training, and without major metabolic, cardiopulmonary, renal, liver, cancer, psychiatric, pregnancy, or medication-related exclusions.
- Sample size: 91
- Age: 20-59 years
- Sex: 27 men and 64 women
- Fitness level: Low physical activity and no regular sports training
- Health status: Adults with overweight or obesity screened for major diseases and contraindications

## Methodology

- Randomized controlled four-arm parallel clinical trial
- 12 weeks
- Real-life mostly self-performed exercise and diet intervention with lab follow-ups
- Randomized and controlled study design.

## Protocol

- Walking HIIT.
- Modality: Self-performed walking intervals.
- Work intervals: 3 min high-intensity walking.
- Recovery: 3 min low-intensity walking.
- Sets or repetitions: 4 intervals in weeks 1-4, 6 in weeks 5-8, 8 in weeks 9-12.
- Intensity: High intervals RPE 18-19; low intervals RPE 9-11.
- Session duration: 31 min, 43 min, then 55 min including warm-up and cool-down as intervals progressed.
- Frequency: 3 sessions/week.
- Program length: 12 weeks.
- Progression: High-intensity intervals increased from 4 to 6 to 8 every 4 weeks.
- VLCHF diet and control conditions.
- Modality: Diet intervention with habitual physical activity, combined diet plus HIIT, or control.
- Intensity: VLCHF: <=50 g/day carbohydrate with increased fat and protein target of 1.5 g/kg lean mass.
- Frequency: Diet daily; HIIT arms 3 sessions/week.
- Program length: 12 weeks.
- Progression: Diet supported with dietitian visits and food logs; HIIT progression as above in combined group.

## Outcomes

### Visceral fat
Status: mixed
Visceral adipose tissue decreased significantly in VLCHF and VLCHF plus HIIT groups, but not in HIIT alone or control.

### Body composition
Status: mixed
Body mass, total fat, trunk fat, waist, and hip measures decreased most clearly in the VLCHF groups; lean mass also decreased in VLCHF groups.

### Exercise capacity
Status: improved
Time to exhaustion improved in HIIT and VLCHF plus HIIT compared with diet-only and control conditions.

### VO2peak
Status: mixed
Relative VO2peak increased most in the VLCHF plus HIIT group, but absolute VO2peak and VT2 did not clearly change.

## Practical Insights

- Walking HIIT can improve treadmill exercise capacity in overfat adults, but this trial did not show HIIT alone reducing visceral fat.
- Body-composition claims in this study are strongly influenced by the dietary intervention.
- Longer 3 min intervals with RPE targets were used rather than short sprint intervals.

## Limitations

- Real-life adherence to diet and activity records was not fully controlled.
- Groups were not fully balanced by sex, and the HIIT group had a slightly higher median age.
- Menstrual cycle and menopause status were not considered.
- Diet cointervention complicates attribution in combined arms.
- HIIT was self-performed for most sessions.

## Safety And Adherence

- The trial used extensive health exclusions. No adverse events were clearly reported in the extracted text.

## Original Sources

- [PubMed](https://pubmed.ncbi.nlm.nih.gov/34993222/) (pubmed)
- [DOI](https://doi.org/10.3389/fnut.2021.785694) (doi)
- [PMC full text](https://www.ncbi.nlm.nih.gov/pmc/articles/PMC8724307/) (full text)

## Agent Guidance

Preserve the paper-level scope of this note. Do not generalize beyond the population, protocol, measured outcomes, and limitations above.