In general, in this study patients presented a linear increase in the mean BMI and decrease in the rate of undernutrition (underweight) over time. The predictors found to have a statistically significant effect on BMI change over the follow-up period via a multivariable linear mixed effect model were:– age in years, residence, marital status, duration of ART, time of follow- up, ART adherence, ART shift, CPT, WHO clinical staging and CD4 count.
The prevalence of undernutrition (BMI < 18.5 kg/m2) was 37% at the six month follow-up and this value declined to 26.6% (at 18 months), 17.9% (at 30 months) and 10.8% (after five years of ART follow up). This finding is consistent with a study conducted in Greece; according to this study, the prevalence of obesity increased from 5.7% at ART initiation to 12.2% after four years of follow-up (10). This greater effect of ART on weight gain or reduction in the proportion of underweight clients may be related to the fact that current drugs are better tolerated and easier to use regimens, resulting in better ART adherence, increased appetite and higher caloric intake (11).
The results of the current study revealed that the mean BMI of ART clients significant improved after the baseline. For example, the mean BMI at baseline was 19 kg/m2 and it reached 21.2 kg/m2 five years after the initiation of ART. This finding is in line with a longitudinal retrospective study conducted in Nigeria, which revealed a significant increase in the median BMI after the beginning of ART (z = 21.864, p < 0.001), with a moderate effect size (r = 0.334). According to this study, the median BMI increased from 22.2 kg/m2 (IQR: 19.8, 24.8) at baseline to 23.4 kg/m2 (IQR: 21.0, 26.4) at 12 months (12). The possible reason for the increase in BMI gain can be attributed to different factors, such as; the advantage of ART in preventing HIV- related opportunistic infections such as wasting syndrome, chronic diarrhea and free access to medical care (13). Overall health improvement and a reduced illness burden can also be among the reasons.
The current study revealed that, being married was associated with a 0.275 kg/m2 lower BMI than being single (β = -0.275, 95% CI; -0.457, − 0.093). This result is supported by a study conducted at Mekele, which reported that being married is associated with a lower BMI by 1.178 kg/m2 than being single (β= -1.178, p < 0.00304) (14). However, a contrary result was reported in a study conducted in South Africa, which reported that, being married/cohabitating was associated with an increase in BMI (ARR = 0.58, P = 0.03) compared with being single (15). This contradictory result might be due to the type of study design used or sociocultural differences between nations, and further investigation is needed.
Place of residence was another predictor that had a positive effect on BMI variation. Compared with clients who reside in rural areas, those who reside in urban areas presented an average BMI increase of 0.767 kg/m2 during the follow-up period (β = 0.767, 95% CI: 0.401, 1.132). This finding is in line with a study conducted in North Ethiopia (β = 0.45, p = 0.000) (16). This difference in weight gain between urban and rural areas could be explained by the different lifestyle factors in urban and rural areas.
This study also revealed that, clients with good self-reported ART adherence had a significant increase in BMI. Thus, the average BMI increased by 0.975 kg/m2 compared with that of clients with poor ART adherence (β = 0.975, 95% CI 0.302, 1.649). This finding is consistent with the findings of a study conducted in Northwest Ethiopia, which reported that, compared with clients with poor ART adherence, those who took the prescribed treatment well or who had at least > 85% good adherence had a 3.988 kg greater mean weight increase (β = 3.988, p < 0.0001) (17). These consistent findings could be explained by a relatively better understanding of life-long care and treatment/chronic care among clients with good adherence, which further improved their weight and body mass index.
According to the results of the present study, a one-month increase in ART duration was associated with a 0.005 kg/m2 increase in the mean BMI (β = 0.005, 95% CI; 0.001, 0.009). Similarly, a previous study in Ethiopia reported similar findings, indicating that duration of ART was significantly association with BMI change (duration β = 0.43, p < 0.001) (5). Another consistent result reported in a study conducted in the United States of America, in which a longer duration of ART, was associated with a greater increase in BMI (P < 0.05) (13).The main reason for the clinical improvement, including a positive change in BMI associated with a longer duration of ART, is thought to be a reduction in the viral load. Patients who stay longer on care and treatment are more likely to develop preventive health behaviour and to receive social support that improves their clinical outcome (18).
With respect to the continuous predictors, in the present study, the coefficient for age indicated that a one-year increase in age, was correlated with a 0.058 kg/m2 increase in BMI (β = 0.058, 95% CI; 0.043,0.072). A study conducted in Switzerland also indicated that BMI change was associated with older age (β = 0.15, P = 0.002) (19). Similarly, another study from Ethiopia reported that the age of respondents was significantly associated with BMI change (β = 0.136, 95% CI; 0.044:0.227) (9). This might be due to changes in body composition and lean body mass in addition to the effects of ART.
According to the current study, those clients without a history of an ART shift from one regimen to another (TDF + 3TC + EFV to TDF + 3TC + DTG was the common shift) were associated with a 0.844 kg/m2 decrease in the mean BMI compared with those with a history of an ART shift (β = -0.844, 95% CI: -1.135, -0.552). This might be because remaining on a suboptimal regimen may not cause clients to gain the expected weight. A similar finding was reported in a study conducted in Burkina Faso, which reported that taking PI-based combination therapy was associated with a decrease in BMI (β= -0.01, p = 0.001) (20). On the other hand, in addition to the previously mentioned studies, a retrospective cohort study conducted in Eswatini (Swaziland) reported that, the BMI rate of change increased by 1.2 kg/m2 (P = 0.001) among clients who had ART shifted to the “DTG’’-based regimen” (21). This is because dolutegravir (DTG) causes significant weight gain, as evidenced by many studies (22). However, no statistically significant association was observed between weight gain and switching to the “DTG’’-based regimen” according to a retrospective study conducted in London (23).
The coefficient for the CD4 + T-cell count revealed that as the CD4 + T-cell count increased by one cell/mm3, the average BMI increased by 0.001 kg/m2 (β = 0.001, 95% CI: 0.001, 0.001 ). A consistent result was reported in a study conducted in the USA, in which patients with a higher CD4 count had an increased BMI (P = 0.001) (13). In addition, this finding is also supported by another retrospective cohort study at Bahirdar, which reported that as the baseline CD4 cell count increased by one cell per mm3, the odds of having a normal BMI for HIV patients increased by 5.4% (AOR = 1.0538, 95% CI:(1.0032, 1.2489), P-value = 0.0231) (24). Another study that was conducted in Switzerland is also in line with the results of the present study; according to the present study, HIV patients with lower baseline CD4 (0–99 and 100–199 cells/µl) had the greatest effect on BMI (β = 1.64, P = 0.001and β = 0.46, P = 0.001 respectively) compared with patients with baseline CD4 level > 350 (19). These consistent findings can be explained by immune recovery or improved immune function, which can lead to better absorption and nutrient utilization, potentially resulting in weight and BMI gain.
The coefficient for WHO clinical staging indicated that being in a higher stage or advanced HIV/AIDS disease (stage III or IV) was associated with a 0.496 kg/m2 decrease in BMI compared with being in a lower WHO clinical stage (stage I or II) (β= -0.496, 95% CI: − 0.548, -0.443). This might be due to the development of OI at advanced stages of diseases, which may lead to increased energy expenditure or negative energy balance. This finding is consistent with a retrospective longitudinal study conducted in Northwest Ethiopia, which reported that, the BMI of clients with advanced WHO stages was 0.6 kg/m2 lower than that of clients with mild stages (β=-0.6, P = 0.002) (25) (24).
Moreover, the results of the current study revealed that, individuals who did not receive CPT had a 0.591 kg/m2 higher BMI than those who received CPT did (β = 0.591, 95% CI 0.365,0.817). This might be because individuals not receiving CPT are stable clients such that their BMI can be higher than that of their counterparts. However, a contrary result was reported in a previously conducted study in Ethiopia, in this study, clients who received cotrimoxazole prophylaxis had an increased BMI compared with patients who did not receive prophylaxis (4). These contradictory findings might be due to individual variation and lifestyle factors and need further study.
The current study revealed that a greater increase in BMI score was observed in the early follow-up periods/visits than in the late visit time after initiating ART. Accordingly, the mean BMI increased by 0.205 kg/m2 as the follow-up time increased by six months (β = 0.205, 95% CI: 0.198, 0.212). This finding is in line with a study performed in Hawasa, Ethiopia, which reported that weight increased by 1.44 kg as the treatment time increased by six months (β = 1.44; 95% CI:1.23–1.66, p < 0.0001) (26, 27). This could be explained; by the fact that with time, antiretroviral combination drugs have started to effectively control replication of the virus so that the number and severity of illnesses decreases which in turn contributes to weight gain.