Research shows that switching kids and teenagers to plant-based diets could prevent a small amount of obesity (0.7% in children, 0.2% in teens), but only if they also eat less food overall. According to Gram Research analysis of 1,153 Portuguese youth, simply adding more vegetables without reducing meat and dairy portions doesn’t help—and can actually increase environmental impact. The most effective approach combines eating more plants with eating less meat, dairy, and sugary drinks while maintaining healthy portion sizes.
Researchers in Portugal studied what 1,153 children and teenagers eat and imagined what would happen if they switched to healthier, planet-friendly diets. They found that eating more plant-based foods could prevent some obesity cases, but only if people also ate less overall. The study shows that simply adding more vegetables isn’t enough—kids and teens need to eat fewer animal products like meat and dairy while keeping their total food intake reasonable. The research suggests the best approach combines eating more plants with eating less meat, dairy, and sugary drinks.
Key Statistics
A 2026 study of 1,153 Portuguese children and teenagers found that switching to plant-based diets could prevent 0.7% of obesity cases in children and 0.2% in adolescents, but only when combined with reduced total food intake.
According to research reviewed by Gram, reducing red meat and dairy consumption in adolescents produced the greatest reductions in greenhouse gas emissions and land use compared to other dietary changes.
A 2026 analysis of Portuguese youth diets found that plant-based eating patterns without portion control actually increased greenhouse gas emissions from 3.9 to 4.1 kg CO2-equivalent per day, demonstrating that food quantity matters as much as food type.
Research on 1,153 children ages 3-17 showed that for younger children, reducing eggs, meat, fish, and soft drinks improved diet quality scores aligned with planetary health principles.
The Quick Take
- What they studied: Whether switching kids and teenagers to healthier, planet-friendly diets could reduce obesity and help the environment
- Who participated: 1,153 Portuguese children ages 3-17 (younger kids ages 3-9 and teenagers ages 10-17) who reported everything they ate for several days
- Key finding: Switching to plant-based diets could prevent a small amount of obesity (0.7% in children, 0.2% in teenagers), but only if people also reduced their total food intake. Interestingly, eating more plants without eating less overall actually increased environmental impact slightly.
- What it means for you: If your family wants to eat healthier and help the planet, focus on eating less meat and dairy while adding more vegetables and plant foods—but don’t just add extra food. The key is swapping out animal products, not eating more overall.
The Research Details
Portuguese researchers collected detailed food diaries and eating records from over 1,100 children and teenagers. They recorded everything these young people ate for several days, including portion sizes. The team then used computer models to imagine different eating scenarios—like what would happen if kids ate less meat, or less dairy, or switched to mostly plant-based foods. They measured three things: how well each scenario matched a healthy planetary diet, how much greenhouse gas pollution the diet would create, and how much land it would require. They also tracked whether these dietary changes could prevent obesity.
The researchers used a special scoring system called the World Index for Sustainability and Health (WISH) to measure how well each diet aligned with the EAT-Lancet reference diet—a scientifically designed eating pattern meant to be healthy for people and the planet. They estimated environmental impact using a database of real-world data about how much pollution and land different foods require to produce.
This research approach is important because it shows real-world eating patterns from actual Portuguese children rather than just theoretical diets. By testing multiple scenarios, researchers could identify which specific food changes would have the biggest impact on both health and the environment. This helps policymakers and families understand that simply promoting plant-based eating without considering total food intake might not achieve the best results.
The study used actual measured data from a national survey rather than estimates, which makes it more reliable. The researchers carefully recorded portion sizes and used validated methods to assess diet. However, the study was conducted in Portugal, so results may differ in other countries with different food cultures. The computer modeling involved assumptions about how people would change their eating, which may not perfectly match real-world behavior.
What the Results Show
When researchers modeled what would happen if Portuguese children and teenagers switched to the EAT-Lancet planetary health diet, they found modest benefits. The biggest obesity reduction came from shifting toward plant-based eating patterns—preventing 0.7% of obesity cases in children and 0.2% in teenagers. However, this benefit only occurred when people also reduced their total food intake.
For younger children (ages 3-9), the most effective changes were reducing eggs, meat, fish, and soft drinks while improving their diet quality scores. For teenagers (ages 10-17), the biggest improvements came from eating less dairy and red meat. These changes reduced both greenhouse gas emissions and land use requirements.
An unexpected finding emerged: when researchers modeled a pure plant-based diet without reducing total food intake, greenhouse gas emissions actually increased slightly (from 3.9 to 4.1 kg CO2-equivalent per day). This happened because the plant-based pattern involved eating more total food than the original diet, even though individual foods had lower environmental impact.
The study revealed that current Portuguese children’s diets are not well-aligned with the EAT-Lancet planetary health recommendations. Most young people eat too much meat, dairy, and processed foods like soft drinks. The research also showed that different age groups benefit from different dietary changes—what works best for younger children differs from what works best for teenagers, suggesting that nutrition guidance should be age-specific.
This research builds on growing evidence that plant-based diets can benefit both human health and environmental sustainability. However, it adds an important nuance that previous studies sometimes miss: simply eating more plants doesn’t automatically help if total food intake increases. The finding aligns with other research showing that portion control matters as much as food type when addressing obesity.
The study was conducted only in Portugal, so results may not apply to children in other countries with different food cultures and available foods. The research used computer models to predict what would happen if people changed their diets, but real people might not follow these changes exactly as modeled. The study couldn’t account for factors like food cost, taste preferences, or cultural traditions that influence what families actually eat. Additionally, the obesity prevention percentages were quite small (less than 1%), suggesting that diet alone may not be sufficient to address childhood obesity without other lifestyle changes.
The Bottom Line
According to Gram Research analysis, families should focus on three changes: (1) Eat less red meat and dairy, (2) Add more plant-based foods like vegetables, legumes, and whole grains, and (3) Reduce total food intake to appropriate portion sizes. This combination approach has the strongest evidence for improving both health and environmental impact. Confidence level: Moderate—the research is solid, but real-world results depend on whether families can sustain these changes.
Parents and caregivers of children and teenagers should pay attention to these findings, especially if concerned about their child’s weight or wanting to make environmentally responsible food choices. School nutrition programs and pediatricians can use this information to guide families. However, these recommendations are general—individual children with specific health conditions should consult their doctor before making major dietary changes.
Changes in weight and environmental impact would likely take several months to become noticeable. Obesity prevention benefits would accumulate over years of consistent dietary changes. Environmental impact reductions would be immediate in terms of what’s purchased, though broader planetary benefits depend on many families making similar changes.
Frequently Asked Questions
Will switching my kids to a plant-based diet help them lose weight?
Plant-based diets may help prevent some obesity cases, but research shows the benefit is small (less than 1%) and only works if you also reduce total food intake. Simply eating more vegetables without eating less meat won’t help with weight. Focus on swapping animal products for plants while keeping portions reasonable.
What specific foods should I reduce to help my teenager eat healthier and help the environment?
For teenagers, research shows the biggest benefits come from eating less red meat and dairy products. For younger children, reducing eggs, meat, fish, and sugary soft drinks has the most impact. Replace these with vegetables, beans, lentils, and whole grains while keeping total food intake appropriate for their age.
Does eating more plant-based foods automatically reduce my family’s environmental impact?
Not automatically. Research shows that eating more plant foods without reducing total food intake can actually increase environmental impact slightly. The key is swapping out animal products for plant foods while maintaining healthy portion sizes—it’s about replacement, not addition.
Are these dietary recommendations safe for all children and teenagers?
These general guidelines are safe for most healthy children, but individual needs vary by age, activity level, and health conditions. Growing children need adequate protein, calories, and nutrients. Consult your pediatrician before making major dietary changes, especially for very young children or those with specific health concerns.
How long will it take to see health benefits from changing my family’s diet?
Weight changes typically take several months of consistent dietary changes to become noticeable. Environmental impact reductions happen immediately in terms of what you purchase, but broader planetary benefits require many families making similar changes. Focus on sustainable changes rather than quick results.
Want to Apply This Research?
- Track daily servings of red meat, dairy products, and plant-based foods (vegetables, legumes, whole grains). Set specific goals like ‘reduce red meat to 2 times per week’ or ‘add 3 vegetable servings daily.’ Monitor portion sizes using the app’s portion guide feature.
- Use the app to plan weekly meals that reduce meat and dairy while increasing plant foods. Create shopping lists that emphasize vegetables, beans, lentils, and whole grains. Set reminders for meal planning and track when you successfully swap a meat-based meal for a plant-based alternative.
- Weekly review of meat/dairy intake trends and plant-based food consumption. Monthly check-ins on portion sizes and total daily calories. Track environmental impact metrics if available (estimated carbon footprint of meals). Quarterly assessment of weight trends and energy levels to ensure changes are sustainable and healthy.
This research provides general information about dietary patterns and their potential health and environmental effects in children and teenagers. It should not replace personalized medical advice from your pediatrician or registered dietitian. Individual nutritional needs vary based on age, activity level, health conditions, and growth patterns. Before making significant dietary changes for your child, especially if they have existing health conditions, food allergies, or are underweight, consult with a qualified healthcare provider. This study was conducted in Portugal and results may not apply equally to all populations. The obesity prevention percentages reported are modest, and diet alone is not sufficient to address childhood obesity without considering physical activity and other lifestyle factors.
This research translation is published by Gram Research, the science division of Gram, an AI-powered nutrition tracking app.