This Common Drink May Do More For Inflammation Than Anyone Expected — & It's Not What You Think
If you've ever reached for a glass of tomato juice thinking it was doing something good for you, new research suggests you might be right: the reasons why are more interesting than you'd expect.
A clinical trial published in Molecular Nutrition & Food Research found that drinking a tomato-soy juice daily for four weeks significantly reduced several markers of inflammation in adults with obesity.
But here's what makes the findings especially interesting: lycopene, the antioxidant that gives tomatoes their red color and usually gets all the credit, may not be the main driver. Other compounds in tomatoes, and the way your gut bacteria process soy, appear to play a meaningful role too.
About the study
Researchers at the USDA's Beltsville Human Nutrition Research Center ran a randomized crossover trial (a study design where each participant tries both interventions, so you can compare how the same person responds to each one) with 12 adults with obesity (BMI 30–45 kg/m²), aged 30–60.
To be eligible, participants had to be non-smokers with no history of daily prescription anti-inflammatory drug use, no recent antibiotic use (within 3 months), no recent use of carotenoid, isoflavone, or metabolism-altering supplements (within 1 month), and no autoimmune or metabolic disorders, gastrointestinal or malabsorption conditions, liver or kidney disorders, or tomato or soy allergies.
Each person drank either a tomato-soy juice or a low-carotenoid control juice every day for four weeks, then switched to the other after a washout period.
The tomato-soy juice delivered 54 mg of lycopene and 189.9 mg of soy isoflavones per day, well above what most people in Western countries typically consume.
The control juice was made from a yellow-flesh tomato variety that naturally produces very little carotenoid content and contained no soy isoflavones, making it a close match to the tomato-soy juice in most other ways.
Blood was analyzed for carotenoid levels and 15 inflammatory proteins called cytokines (chemical messengers your immune system uses to signal inflammation).
Urine was also collected and analyzed using a technique called untargeted metabolomics, essentially a broad scan of the compounds your body excretes, to track how each intervention affected the body's metabolic activity.
Three inflammatory markers dropped — but the picture is complicated
After four weeks on the tomato-soy juice, three pro-inflammatory cytokines, IL-12p70, IL-5, and GM-CSF, were significantly reduced.
TNF-α, a key driver of chronic inflammation in obesity, also trended downward, nearly reaching statistical significance (p = 0.052). These reductions were not seen during the control juice period.
Plasma lycopene increased to an average of 1,298.4 nmol/L following tomato-soy intake, a 2.48-fold increase from pre-intervention levels. Plasma beta-carotene also increased significantly, reaching a 2-fold average increase compared to pre-tomato-soy levels.
One important nuance is that the cytokine reductions appeared when comparing participants' results before and after the tomato-soy period, but not when directly comparing the tomato-soy and control groups at the end of each intervention.
The researchers think this pattern still points to a real anti-inflammatory effect from the tomato-soy juice, but they're careful to note that the study was smaller than originally planned: it was designed for 30 participants, but COVID-19 disrupted enrollment. That limits how definitive the conclusions can be.
It's not just lycopene doing the work
One of the more surprising findings came from the urine analysis.
Both the tomato-soy juice and the low-carotenoid control juice produced some of the same changes in what participants were excreting, specifically, increases in naringenin glucuronides (a compound derived from a flavonoid naturally found in tomatoes) and several breakdown products of phenolic acids (plant-based compounds found in tomatoes that get metabolized by your gut).
In animal studies, naringenin has been shown to reduce inflammatory markers in fat tissue, including TNF-α. A separate cell study found that physiological levels of naringenin and its related compounds affected inflammatory gene activity in human immune cells.
The researchers also found a significant reduction, roughly 50%, in a type of fatty acid metabolite called a medium-chain acylcarnitine, which tends to be elevated in people with low-grade chronic inflammation like obesity. This reduction happened after both tomato interventions, not just the tomato-soy one.
That suggests phytochemicals in tomatoes beyond lycopene may be contributing to the anti-inflammatory benefits of tomato foods, and that those benefits may be broader than previously appreciated.
Your gut microbiome shapes how you respond to soy
The urine data also revealed something important about soy: how your body responds to it depends heavily on which gut bacteria you have.
After tomato-soy intake, urine profiles were dominated by metabolites derived from daidzein, genistein, and glycitein, the main isoflavones in soy, along with compounds produced when gut bacteria break those isoflavones down further.
Among the most notable findings: ethylphenol sulfate isomers, produced when gut microbes metabolize genistein, increased roughly 96- to 173-fold in urine after tomato-soy intake compared to pre-intervention. O-DMA glucuronides, derived from daidzein via gut microbial metabolism, were also significantly elevated.
Individual responses varied considerably. About 17% of participants produced equol, a compound made from daidzein by specific gut bacteria (from the Coriobacteriaceae family), which aligns with prior estimates that roughly 25–30% of Western adults are "equol producers."
The equol producers in this study showed different metabolic patterns compared to non-producers, reinforcing the idea that your gut microbiome composition shapes how you respond to soy foods.
The bigger picture
This study adds to a growing body of evidence that whole foods work through complex, interconnected mechanisms rather than through a single "hero" nutrient.
Tomatoes contain dozens of phytochemicals beyond lycopene, including flavonoids like naringenin and a range of phenolic acids. Soy isoflavones, meanwhile, are transformed by gut microbes into metabolites that may carry their own biological activity.
The researchers note that each pro-inflammatory cytokine reduced in this study is regulated in part by the NF-κB signaling pathway, a key molecular switch involved in chronic diseases including obesity-related inflammation.
Prior research has shown that both lycopene and soy isoflavones can dial down this pathway in obesity models, though the authors caution that inflammatory mechanisms are highly interconnected and more research is needed.
Originally developed in the context of prostate cancer research, tomato-soy juice is now showing promise across a broader range of inflammation-related conditions, including obesity. The authors call for future clinical and mechanistic studies to better understand these effects.
What this means for your plate
You don't need a specialized functional food product to apply the takeaways here. A few practical points worth keeping in mind:
- Tomato products still deliver: Processed tomato products like juice and sauce can provide meaningful amounts of lycopene and other phytochemicals. In fact, lycopene is more bioavailable from heat-processed tomatoes than from raw ones.
- Pair tomatoes with soy: The combination of tomato and soy compounds, working through complementary pathways, may offer more than either food alone.
- Your gut microbiome matters: How you respond to soy foods depends in part on which gut bacteria you have. Supporting a diverse microbiome through a varied, plant-rich diet may help you get more out of these foods.
- Think beyond single nutrients: The evidence here supports eating whole foods rather than chasing isolated compounds. The full range of phytochemicals in tomatoes and soy appears to matter.
The takeaway
A new clinical trial found that drinking tomato-soy juice daily for four weeks reduced key inflammatory markers in adults with obesity, and the benefits appear to come from more than just lycopene.
Other tomato phytochemicals and gut-transformed soy metabolites likely play a role, pointing to the value of whole-food combinations over isolated nutrients.
While the study was small and more research is needed, it adds meaningful evidence that tomato and soy foods may support healthier inflammatory pathways in the context of obesity and metabolic health.