Like telling starving French peasants to eat cake, Robert F. Kennedy Jr.’s strategy for reducing obesity — addressing lifestyle — is absurdly out of touch with Americans’ reality. While Congress considers confirming him as health and human services secretary, brain science leaves no room for debate that the “let them eat kale” strategy will fail.

Surviving day to day takes every ounce of mental and physical resources for millions of Americans. For the bottom 40% of U.S. households ranked by income, almost 40% of take-home pay goes to housing and 15% goes to food (according to 2023 consumer expenditure data available from the Bureau of Labor Statistics site).

Stretching, juggling and hustling to meet all of the other basic survival needs leaves nothing for carefully considering what to have for dinner.

According to the book “Scarcity: Why having too little means so much,” “Scarcity directly reduces [mental] bandwidth — not a person’s inherent capacity, but how much of that capacity is currently available for use.” For example, a person coping with scarcity performs worse on intelligence tests. Relieved of scarcity, the person’s score improves.

A brain preoccupied with scarcity has more influence over the body’s health than better diet or more exercise. Thus, even if we could foist “healthy choices” onto people, strenuous coping takes away the benefits.

Imagine a gourmet meal delivery service that is free for everyone. The bottom 40% of households’ health would not improve the way it would for high-income folks. A randomized controlled trial of the Mediterranean diet provided the same food to everyone and found that high- income people improved their cardiovascular health, while low-income people did not.

Likewise, the impact of physical exercise varies for the rich and the poor. The poor still had worse health than the rich, after they all did the same exercise program in this randomized controlled trial.

Rich and poor people get different results because health is largely shaped by how a person and his brain interact with the world. As Arline Geronimus describes in her book “Weathering,”  “ … healthy aging is a measure not of how well we take care of ourselves but rather of how well society treats and takes care of us.”

How well society treats a person shows up in big and small ways.

For example, we expect high-paying jobs to offer health insurance, and we accept that low-paying jobs do not. In 2023, only 4% of adults had no health insurance in households earning at least 400% of federal poverty, compared to 16% of adults in households earning less than that. The low-income worker spends energy worrying about how, when and where to get medical care. This is just one tiny social construct of  thousands that support or harm a person’s health, and that shape health more strongly than a person’s own behaviors.

When a large share of our people spend their time, energy and intellect on getting by, we cannot expect “let them eat kale” to make them healthy. How our society treats people is far more powerful than how people treat themselves. Until we change that, no amount of kale will do anything.