Have you ever come across the term ‘skinny fat’? The health risks of excess body fat aren’t reserved for those who are classified as overweight and obese. Some people are within a healthy weight range but still have a higher body fat percentage.
It’s well established that high protein diets can help with weight loss. But can a high-protein diet reduce excess body fat in women with a ‘healthy’ body weight?
Background
Normal weight obesity, or NWO, is defined as having a normal body weight and BMI, but a body fat percentage >30% for women or >20% for men. Like overweight and obesity, NWO is associated with a higher risk of metabolic diseases.
Studies have found that women with NWO have a lower resting metabolic rate due to lower lean body mass. Preserving muscle mass is critical for these women to reduce body fat.
Elevating protein intake has been shown to be effective at reducing body weight in overweight and obese subjects. It is also an intervention that can prevent declines in lean body mass. However, there is limited literature exploring the effects of a high-protein diet on women with NWO.
The study
Researchers designed a study to evaluate the effects of a high-protein diet on body composition and appetite in women with NWO. The study was 12-week double-blind randomised controlled trial.
Participants were women between 30-60 years with a BMI between 18.5-25 and a body fat percentage of >30%. Exclusion criteria including smoking, use of birth control within 6 months, pregnancy and lactation, drug use, and history or current chronic disease including thyroid, GI, kidney, type 2 diabetes and psychiatric disorders. Those who were already following a high protein diet, using protein supplements or consuming a high intake of caffeine (>250mg/day) were also excluded.
50 participants took part. They were randomly allocated to a high-protein (HP) or standard-protein (SP) diet group. The HP group consumed 25% of energy from protein, and the SP group consumed 15% of energy from protein. Both diets were eucaloric.
Researchers assessed body weight, fat mass, lean body mass, waist circumference and appetite of participants at baseline and 12 weeks.
The findings
After excluding participants who did not participate in follow-up or adhere to the dietary interventions, results were collated from 24 in the HP group and 23 in the SP group.
At 12 weeks, the lean body mass was higher in the HP group compared to the SP group, which saw no significant changes.
The HP group also had a lower fat mass, body fat percentage and waist circumference compared to the SP group.
Both groups saw no significant changes in appetite or body weight.
Conclusions
The researchers concluded that a 12-week high protein diet in women with NWO significantly improved body composition, but did not lead to weight loss.
Some limitations of the study were noted. These included the methods analysing appetite changes and the lack of urine samples to monitor compliance with the high protein intake.
The study was specific to women between 30-60 and excluded many common health conditions. Therefore, further research looking into the influence of macronutrients in NWO are needed to make broader conclusions.
Reference
Haghighat, N., Ashtary-Larky, D., Bagheri, R., Mahmoodi, M., Rajaei, M., Alipour, M., Kooti, W., Aghamohammdi, V. and Wong, A., 2020. The effect of 12 weeks of equicaloric high protein diet in regulating appetite and body composition of women with Normal Weight Obesity: a randomized controlled trial. British Journal of Nutrition, pp.1-20.