Weight Loss and Immune Function

 

    To lose weight is one of the common new-year-resolutions for many. The springtime is the season for people to put their actual weight loss efforts into action.  It is a good decision to lose the extra weight to boost immune function in a long run, however, the common weight loss practices such as fasting and/or exercising if overdone, it may hurt the immune system than improve it. The last thing you would want to do in the middle of the global spread of coronavirus is to compromise your immunity.

 

    The relationship between adequate nutrition and immune function has been repeatedly demonstrated. Mice studies provided strong evidence that energy extremes, including energy restriction and diet-induced obesity, have deleterious effects on the immune response to influenza infection. Both energy restriction and diet-induced obesity mice demonstrate increased susceptibility and mortality to influenza infection. There are striking similarities between energy restriction and diet-induced obesity during influenza infection, including impaired natural killer cell function and altered inflammation (1).

   

    Ten overweight women participated in a weight-loss study which reduced their 50% energy intake daily for 84 days (2). By the end of the study, these women lost an average of 7 or 9 kg of body weight on either low-fat diet or high-fat diet. However, the energy restriction caused a significant decrease in the serum concentration of IgG, IgA, C3, and the number of circulating natural killer cells, which are all immune parameters. They increased food intake for 35 days after the energy restriction period so that they could maintain the bodyweight, which reversed some of the decreases in immune parameters caused by energy restriction, but these immune parameters did not return to pre-restriction levels. These authors concluded that the health status of the women in the study did not seem to be compromised; however, it could be compromised under more drastic restrictions or with moderate restrictions in high-risk subjects (2). In my opinion, reduce 50% of food intake for weight loss is not a healthy way, which is severe restriction and the lowered number of natural killer cells at the end of the weight loss study had already indicated the immune system in these women had been compromised. The critical role that natural killer cells play in controlling virus infection, including influenza, has been well-established (1).

 

    Food restriction is an effective strategy for weight loss. However, food restriction can alter biological rhythms and leads to physiological stress. Whether food restriction frequency can have different health outcomes was investigated by a group of scientists (3). Mice were fed a high-fat diet for 8 weeks to make them obese, and then they were randomly divided into three groups: the control group was continuously fed the high-fat diet; the two food restriction groups were fed 50% of food consumed by the control mice with one group (FR1) being fed the full amount once a day, and the other group (FR2) being fed the same total amount as FR1 twice a day for 3 days. To examine the effects of long-term, dietary restriction, mice were given restricted food as for the FR1 and FR2 protocols for 3 days, and then food was unrestricted for the following 4 days. The alternating restricted/unrestricted diet was given for a total of 8 weeks. The severe food restriction induced an increase in stress hormone levels, and this was exacerbated by infrequent feeding. When food restriction coupled with infrequent feeding was repeated over many weeks, the alternating FR1 group showed impaired glucose tolerance compared with the alternating FR2 group (3). This study suggested that for weight loss, it would be better to reduce the food intake throughout all the meals than cutting off the number of meals in a day.

 

    Exercise is another effective way that people often use to lose weight. Many components of the immune system may exhibit adverse change after prolonged, heavy exertion of exercising. These immune changes occur in several compartments of the immune system and body, e.g. the skin, upper respiratory tract mucosal tissue, lung, blood, and muscle. Most exercise immunologists believe that during this 'open window' of impaired immunity after extensive exercise, which may last between 3 and 72 hours, viruses and bacteria may gain a foothold, increasing the risk of subclinical and clinical infection. The infection risk may be amplified when other factors related to immune function are present, including exposure to novel pathogens during travel, lack of sleep, severe mental stress, malnutrition or weight loss (4). Yes, too much exercise can impair immune function. If it is combined with inadequate nutrition and/or weight loss, the immune system would be even further compromised.

 

    A nutritious diet is essential for good health, especially so if you are on a restricted diet or increase your exercise intensity for weight loss. For weight loss, we need to pay attention to a holistic approach to include changes for healthy diet intake and lose weight in a way not to hurt our health. I hope that this blog can help you to pay attention to the healthy way of weight loss to preserve immunity. For people who would like to learn more about how to lose weight healthily and how to boost immune function, you are welcome to contact me via email.

 

References:

1. Gardner EM, Beli E, Clinthorne JF, Duriancik DM. Energy intake and response to infection with influenza. Annu Rev Nutr. 2011. 31:353-67.

2. Kelley DS, Daudu PA, Branch LB, Johnson HL, Taylor PC, Mackey B. Energy restriction decreases number of circulating natural killer cells and serum levels of immunoglobulins in overweight women. Eur J Clin Nutr. 1994. 48(1):9-18.

3. Lee YS, Lee C, Jun HS. Infrequent Feeding of Restricted Amounts of Food Induces Stress and Adipose Tissue Inflammation, Contributing to Impaired Glucose Metabolism. Int J Med Sci. 2018. 15(14):1667-1675.

4. Nieman DC. Special feature for the Olympics: effects of exercise on the immune system: exercise effects on systemic immunity. Immunol Cell Biol. 2000.78(5):496-501.