The effect of higher protein intake during energy restriction‐induced weight loss on counts of intermediate and classical monocytes and their relations to lipid‐lipoprotein profile and C‐reactive protein
Authors: Lin Ge , Kim Jung Eun , Zhou Jing , Campbell Wayne W 
Published: November 2023

Background

Monocyte subsets, intermediate monocyte (IM) and classical monocyte (CM) in particular, are important biomarkers of cardio‐metabolic disease. Limited studies suggest that purposeful weight loss induces a reduction in monocyte counts and improvements in inflammation and cardio‐metabolic risk factors. Also, consuming a high‐protein diet is suggested to improve cardio‐metabolic risk factors, but the effect of a high‐protein diet on the counts of monocyte subsets during weight loss remains unknown.

Purpose

The purpose of this study was to assess the effect of a high‐protein diet on counts of IM and CM in overweight/obese adults after energy restriction (ER). In addition, the relations between monocyte counts and lipid‐lipoprotein profile and C‐reactive protein (CRP) were examined.

Method

A total of 33 middle‐aged adults (9 M and 24 F, age: 52 ± 1y, BMI: 30.5± 0.5 kg/m2, mean ± SE) consumed an energy‐balance diet with normal protein (0.8 g protein•kg baseline body mass−1•d−1) for 3 weeks (baseline). They then consumed either a normal protein (NP, n=18) or high protein (HP, n=15) (0.8 vs. 1.5 g•kg−1•d−1) ER diet (750 kcal/d deficit) for 16 wk (post‐intervention). The HP was achieved by consuming additional 0.7 g•kg−1•d−1 of milk protein isolate. At baseline and post‐intervention, subjects’ whole blood samples were collected when they were fasting and the counts of IM (CD14++CD16+) and CM (CD14++CD16−) were analyzed using multi‐parameter flow cytometry. Fasting‐state plasma samples were also collected to measure CRP and lipid‐lipoprotein profile. The main effects of time (ER) and group (protein intake)*time interaction on IM and CM counts were assessed using repeated measures ANOVA, adjusting for age and gender. A multiple linear regression model was used to assess associations between monocyte counts and CRP and lipid‐lipoprotein profile parameters with estimates adjusted for age and gender.

Results

The counts of IM and CM were not different between NP and HP at baseline and post‐intervention. Over time, IM count decreased (baseline: 0.015 ± 0.002; post‐intervention 0.007 ± 0.002 K/CUMM, p < 0.001), but CM count was not changed. These responses were not influenced by protein intake.

Using data from both groups at baseline and post‐intervention, IM count was positively related with total‐cholesterol (TC), low‐density lipoprotein‐cholesterol (LDL), TC/high‐density lipoprotein‐cholesterol (HDL) ratio, and LDL/HDL ratio, but not triglyceride, HDL or CRP. CM count was positively related with only CRP. Over time, changes in IM and CM counts were not associated with changes in lipid‐lipoprotein profile or CRP.

Conclusion

These results confirm that relation between intermediate monocytes count, an important biomarker of cardio‐metabolic disease, and indices of systemic lipid‐lipoprotein quality. Also, the energy‐restriction induced improvement in intermediate monocyte count may be achieved by consuming either a normal or high‐protein diet.

Support or Funding Information

National Dairy Council, Purdue Ingestive Behavior Research Center, and NIH UL1TR001108