Need a Boost? Trans Fat in Milk Enhances Immunity

Written by: Brittany T. Truong, Ph.D. | Issue # 134 | 2026

Breast milk is known to have a positive effect on the immune system. Previous studies have shown that breastfed infants have an expansion of regulatory T cells compared with infants who are formula fed [1]. Other studies have shown that breastfeeding lowers a child’s risk of developing asthma by promoting a healthy gut microbiome [2].  

Human breast milk is incredibly complex. It is composed of many carbohydrates, fatty acids, protein, antibodies, anti-inflammatory cytokines, and beneficial bacteria. Together, these molecules support the baby’s development. 

However, researchers at the University of Chicago asked whether there was a sole molecule in breast milk that could singlehandedly shape an infant’s immune system [3]. 

In a new study published earlier this year in Science, these researchers found that trans-vaccenic acid (TVA), the most abundant trans fatty acid in breastmilk, promotes T-cell expansion during infant development and leads to an earlier, more effective response to viral and bacterial infections in mouse models [3]. 

This team had previously shown that TVA directly promotes cytotoxic T cells and anti-tumor immunity in adult mice [4]. Given its abundance in breast milk, they hypothesized that it may play a substantial role in neonatal immune development as well. 

Humans and mice cannot produce TVA on their own and must obtain it by consuming foods such as lamb, beef, or dairy products. 

The researchers gave nursing female mice either a control diet or food supplemented with TVA at the beginning of pregnancy. Compared with the control group, pups fed milk from the TVA females had a larger spleen and thymus, both important organs in the immune system [3]. 

To understand what was happening on a cellular and molecular level, the team performed single-cell multiomic analyses and genetic manipulations. They found that pups who nursed on TVA-supplemented milk had an expansion of T cells compared with the control group. The TVA blocks GPR43, a G-protein coupled receptor that suppresses the immune system. In doing so, the TVA promotes an upregulation of genes involved in promoting T-cell maturation, function, growth, survival, and migration [3]. 

To determine whether the T cells were functional, the researchers then infected the pups with H1N1 influenza virus. Pups who had been fed milk from TVA mothers had better survival rates, lower viral loads, and reduced lung damage compared with controls. Similarly, when the researchers infected pups with Salmonella, those fed TVA-supplemented milk had reduced bacterial colonization in the spleen and liver [3]. 

This enhanced ability to fight viral infections carried over into adulthood, suggesting that TVA supports long lasting immunity. 

Another round of single-cell multiomics showed that compared with the control group, following H1N1 infection, pups taking TVA-supplemented milk had more Th1-like cells, a subset of T cells that helped clear the viral loads earlier and more effectively [3]. 

The researchers then asked if there was an optimal time window in which pups must be exposed to TVA in order to build their immunity. 

First, they used a mouse fostering strategy. Pregnant mice received a control or TVA-supplemented diet, but after the pups were born, the researchers swapped mothers. Serum TVA was only detected in pups who had nursed from TVA mothers. These pups also had reduced viral loads, suggesting that postnatal TVA exposure was important for immune system programming [3]. 

Then, the researchers tested whether TVA had any effect on the immune system after weaning. They gave TVA-supplemented diets to adult mice and found that it did not enhance their ability to produce more T cells or fight off a viral infection [3]. 

Together, these data suggest that reprogramming the immune system is limited to neonatal TVA exposure. 

This study offers key insights into how maternal diet can play a key role in neonatal development. Mothers may be tempted to consume diets rich in trans fats to help ensure their babies are exposed to more TVA and boost their immune systems; however, the source matters as industrial trans fats can be harmful while dairy-derived trans fats are associated with potential health benefits. We’ve long known the benefits of dairy consumption for lactating mothers [5]. This study suggests that moms’ dairy intake may have another unexpected benefit for their babies’ immune system.

References

1. Wood H, Acharjee A, Pearce H, Quraishi MN, Powell R, Rossiter A, et al. Breastfeeding promotes early neonatal regulatory T-cell expansion and immune tolerance of non-inherited maternal antigens. Allergy. 2021 2021/08/01;76(8):2447-60.
2. Shenhav L, Fehr K, Reyna ME, Petersen C, Dai DLY, Dai R, et al. Microbial colonization programs are structured by breastfeeding and guide healthy respiratory development. Cell. 2024;187(19):5431-52.e20.
3. Fan H, Zheng Z, Oliphant K, Li J, Mack R, Ju CW, et al. Maternal trans-vaccenic acid shapes neonatal T cell development and early-life immune imprinting. Science. 2026 Jun 18;392(6804):eaea4041.
4. Fan H, Xia S, Xiang J, Li Y, Ross MO, Lim SA, et al. Trans-vaccenic acid reprograms CD8+ T cells and anti-tumour immunity. Nature. 2023 Nov;623(7989):1034-43.
5. Dairy for mom & baby [Internet]. Syracuse (NY): American Dairy Association North East; [Cited 2026 August 11]. Available from: https://www.americandairy.com/health-wellness/benefits-of-dairy/dairy-for-mom-and-baby/.

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