Nutrition is often reduced to a number – calories in versus calories out. Yet research across species is revealing that what we eat and when we eat it have profound consequences for reproductive health, ageing and disease susceptibility. Our recent study in the fruit fly Drosophila melanogaster adds new evidence to a growing body of work showing that the balance of macronutrients and the timing of dietary exposure program life-history traits in ways that echo across evolutionary biology and human public health.
The Fly Experiment
We reared an outbred population of Drosophila on isocaloric diets differing in protein and carbohydrate ratios. Male flies raised on carbohydrate-rich developmental diets grew larger wings – a proxy for adult body size – than those reared on protein-rich diets. In adulthood, protein-rich diets at both stages increased fertility for male-female pairs, reaffirming the key role of dietary amino acids in reproductive output. Longevity responses, however, were strikingly sex-specific. Males lived longer when they experienced carbohydrate-rich diets during development, but adult intake of such diets reduced lifespan in both sexes. Stress resistance traits – survival under starvation or desiccation – were little affected by developmental diet yet improved when adult diets were carbohydrate-rich. Most traits showed additive contributions of development and adult diet, but male starvation resistance displayed a weak interaction: adult benefits of carbohydrate-rich diets were greater when development had occurred on protein-rich food.
Unlike earlier studies showing that reproduction and survival depend on dietary protein-tocarbohydrate ratios (e.g., Drosophila optimizing reproduction at 1:4 and survival at 1:16), our full-factorial experimental design showed how developmental diets shape adult outcomes in the context of contrasting adult diets, and vice versa, highlighting not only the quantity of calories but also the quality and their timing across life stages that governs life-history outcomes. This in turn raises important new questions about the mechanisms through which early diet history shapes adult health, opening promising avenues for future research.
Early Diet Sets the Stage
Why does a larval diet of extra sugar or protein reverberate through an adult fly’s entire life? In evolutionary biology the answer lies in timing. Natural selection cares most about traits that affect survival and reproduction early on; its influence wanes with age. As a result, alleles that are beneficial early but harmful later can accumulate – a concept known as antagonistic pleiotropy. Early nutritional environments can thus shape lifelong fitness by influencing gene expression, hormonal pathways and organ development.
This notion resonates with the Developmental Origins of Health and Disease (DOHaD) hypothesis in humans. Reviews of the epidemiological literature reveal that both deficiency and excess nutrition in early life cause epigenetic changes with effects that last a lifetime and contribute to chronic diseases. The first 1,000 days of life – from conception to the second birthday – are a critical window when tissues and regulatory systems are “programmed.” Malnutrition or high-calorie, low-quality diets during this period predispose individuals to obesity, metabolic syndrome and type 2 diabetes when later exposed to energy-dense environments. Conversely, adequate nutrition and breastfeeding reduce the risk of chronic disease. Neuroscientists note that during this window the brain forms up to 1,000 neural connections per second; poor maternal and child nutrition can impair cognitive development and lead to stunting that persists across generations.
A Pandemic of Poor Diets
Non-communicable diseases now dominate India’s health landscape, accounting for roughly 60 % of all deaths. Among them, diabetes is rising fast. NFHS-5 finds that 6.5 % of adults have diabetes, and subsequent analyses using the same data suggest the true prevalence could be closer to 16 % when undiagnosed cases are included. At the same time, over a quarter of adults are overweight or obese, with urban rates far exceeding rural ones. Globally, high body-mass index was linked to 4 million deaths in 2015, the majority from cardiovascular disease. Yet India still has the world’s largest burden of child under-nutrition: about 40.6 million children are stunted, representing one-third of the global total. This dual burden — excess on one end and deficit on the other — underscores that simply counting calories is not enough; the quality and balance of proteins, carbohydrates, fats and micronutrients matter profoundly for health across the life course.
Balancing Macronutrients and Designing Policies
Research in fruit flies and mammals shows that it is not just the amount of food but its composition that shapes health. When male fruit flies were given diets with a low protein-to-carbohydrate ratio during their development, they lived longer but the same diet during adult stage promoted survival under starvation and desiccation stress but at the expense of lifespan and reproductive output. Mice on low-protein, high-carbohydrate regimens displayed better late-life cardiometabolic health than those on calorie-restricted diets. Such findings caution against simply counting calories.
Translating such insights into policy requires an emphasis on when and what people eat. India’s Poshan Abhiyaan (National Nutrition Mission) embodies this shift. It targets the first 1000 days of life and fields about 1.4 million Anganwadi workers, reaching more than 80 million women and children. In its initial phase, stunting in the mission’s focus states fell from 41 % to 37 % and wasting from 22 % to 20 %—proof that early-life nutrition interventions work. To build on this, consumer-awareness drives such as the food-label literacy campaigns promoted by the Food Safety and Standards Authority can help families make better choices, especially when paired with hands-on education. Simple classroom experiments with fruit flies, for example, can show in real time how sugary versus protein-rich diets alter growth and behaviour, dovetailing with the National Education Policy’s call for inquiry-based learning. Coupling such educational efforts with subsidies for pulses, fruits and vegetables, curbs on marketing ultra-processed foods and label-reading instruction in school and community programmes would reinforce one another and move India toward a future where children are neither stunted nor overweight and adults enjoy longer, healthier lives.
A Call to Action
In a world battling both undernutrition and obesity, families, clinicians and policymakers must move beyond calorie counting to embrace dietary quality and timing. Investing in the nutrition of mothers and young children – with adequate proteins, complex carbohydrates, healthy fats and micronutrients – is not only compassionate but also strategic: it builds healthier societies, more productive economies and more resilient ecosystems.
(Mohankumar Chandrakanth is a Ph.D. student and Sudipta Tung is Wellcome Trust-DBT India Alliance Early Career Fellow, Department of Biology - both from Ashoka University.)
Views are personal, and do not represent the stance of this publication.
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