This is a randomized controlled pilot study to evaluate the effects of intermittent caloric restriction compared with low carbohydrate diet in youth with cardiometabolic risk.

The National China Health and Nutrition Survey revealed that 42% of overweight children had at least one cardiovascular metabolic risk, such as hyperglycaemia, dyslipidemia or hypertension. Non-pharmaceutical life style modifications are the recommended intervention to these subjects, including caloric restriction and increased physical activity. However, the problems of poor compliance and metabolic adaptation are well known. Evidences from a number studies in rodent models and human indicated that intermittent caloric restriction (ICR) may stimulate series reactions in human body, including improvement of insulin sensitivity, blood pressure, oxidative stress and inflammation, and may be easier to follow. Evidence from larger human studies is strongly encouraged, while the effects, safety and adherence in chidren and youth need to be studied.

This study is a randomized controlled trial of intermittent caloric restriction versus low carbohydrate diet in youth with cardiometabolic risk over one month period. The intervention is based on the 5:2 diet, which involves caloric restriction for 2 days (consecutive or nonconsecutive, 600kcal/d for male and 500kcal/d for female) per week and unrestricted eating during the other 5 days of the week. For control group, the subjects receive 7 days (consecutive or nonconsecutive) of low carbohydrate diet intervention during the 14-day intervention period,. Carbohydrate intake of low-carbohydrate diet should be controlled as ≤ 50g per day. Total trial duration is one month consisting of a 14-day intervention phase and a 14-day self-maintenance phase. During the maintenance phase, two follow-up electronic questionnaires were conducted.

The study aim to explore effects of the dietary interventions on cardiometabolic markers, inflammatory reaction, oxidative stress and gut microbiome in youth with cardiometabolic risk.

Inclusion Criteria:

Have at least one of the following cardiometabolic abnormalities:

1. Overweight or obesity (central obesity or general obesity)
2. Prediabetes: impaired fasting glucose (IFG) and/or impaired glucose tolerance (IGT)
3. Dyslipidemia
4. Elevated blood pressure

Criteria for cardiometabolic abnormalities:

1. Overweight or obesity

   For subjects (9 ≤ age ≤ 18 years) :

   • General obesity: Body mass index higher than the 85th percentile for overweight and the 90th percentile for obesity, based on the references for screening overweight and obesity in Chinese children and adolescents.

   • Central obesity: Waist circumference higher than the 90th percentile of the age and gender-specific reference for screening cardiovascular risk factors in Chinese children and adolescents.

   For subjects ( 19 ≤ age ≤ 30 years) :

   • General obesity: Body mass index between 24.0 and 27.9 kg/m2 for overweight and ≥28 kg/m2 for obesity.

   • Central obesity: Waist circumference ≥85cm for men and ≥80cm for female. Based on recommendation of overweight and obesity in Chinese adults.

2. Prediabetes:

   With IFG and/or IGT. IFG: fasting glucose from 5.6 to 6.9 mmol/L; IGT: 2-h glucose in the 75g oral glucose tolerance test from 7.8 to 11.0 mmol/L.

   Based on recommendation of American Diabetes Association.

3. Dyslipidemia:

   For subjects (9 ≤ age ≤ 18 years) :

   Triglycerides of ≥1.70 mmol/L or total cholesterol of ≥5.18 mmol/L or lowdensity lipoprotein cholesterol ≥3.37 mmol/L or highdensity lipoprotein cholesterol of ≤1.04 mmol/L. Based on recommendation in Chinese children and adolescents.

   For subjects ( 19 ≤ age ≤ 30 years) :

   Triglycerides of ≥1.7 mmol/L or total cholesterol of ≥5.2 mmol/L or lowdensity lipoprotein cholesterol ≥3.4 mmol/L or highdensity lipoprotein cholesterol of ≤1.0 mmol/L. Based on guideline for the management of dyslipidemia in Chinese adults.

4. Elevated blood pressure:

For subjects (9 ≤ age ≤ 18 years) :

Blood pressure higher than the 90th percentile of blood pressure age and gender-specific reference standards for Chinese children and adolescents, or blood pressure >120/80 mmHg.

For subjects ( 19 ≤ age ≤ 30 years) :

Systolic blood pressure≥120 mmHg and/or diastolic blood pressure ≥80 mmHg. Based on Chinese guidelines for the management of hypertension.

Exclusion Criteria:

1. Diagnosis of severe diseases such as cardiac insufficiency, severe malnutrition or immunodeficiency.
2. History of bariatric surgery.
3. Use of antiobesity drugs or supplements.