Holiday season impact on body composition and market trading patterns

The weeks between Thanksgiving and New Year’s bring subtle shifts in both physiology and finance. A study of college students found that while overall body weight stayed stable, body fat percentage rose noticeably over the holiday stretch [1]. At the same time, traders continue to debate whether a “holiday effect”—higher market returns before federal holidays—actually exists, with mixed evidence from systematic analyses of S&P 500 data [2].

Key takeaways

• Average body weight of college students did not change significantly from pre‑Thanksgiving to post‑New Year’s (71.3 kg vs. 71.2 kg) [1].
• Percent body fat increased from 25.9 % to 27.0 % and fat mass grew from 18.3 kg to 19.1 kg over the same period [1].
• Market researchers observe a modest average daily SPY gain of 0.04 % and use this as a benchmark to test holiday‑related outperformance [2].
• Analyses compare returns from buying SPY several days before holidays to random holding periods, seeking evidence of excess gains [2].
• The existence of a reliable holiday trading edge remains uncertain, with explanations ranging from investor optimism to reduced liquidity [2].

Body composition shifts during the holiday break

The longitudinal study tracked 82 healthy college students through three visits: before Thanksgiving, shortly after the holiday, and within ten days after New Year’s. Weight measurements showed no statistically significant change (P = 0.71), suggesting that the festive period did not cause overall mass gain. However, dual‑energy X‑ray absorptiometry revealed a rise in percent body fat (P < 0.01) and an increase in absolute fat mass (P < 0.01), while fat‑free mass remained essentially unchanged (P = 0.08). The researchers noted strong positive correlations between changes in BMI and both fat and lean tissue metrics, indicating that body composition can shift even when the scale reads the same. These findings imply that holiday indulgences may preferentially add adipose tissue rather than muscle, a nuance that weight alone can mask.

Market analysts probe the “holiday effect”

Separately, systematic traders have long speculated that markets tend to rally in the days leading up to U.S. federal holidays. One analyst compiled daily SPY returns from 1993 to 2026, establishing an average daily gain of roughly 0.04 % as a baseline for market beta. To test the holiday hypothesis, the analyst measured returns when buying SPY a set number of days before each holiday and selling on the last trading day before the break, then compared those results to returns from randomly timed trades of equal length. Visual data showed the holiday‑timed returns (blue dots) versus random returns (orange dots), but the narrative stopped short of a definitive conclusion, leaving the existence of a consistent, exploitable edge ambiguous. Proposed explanations for any observed uplift include heightened investor optimism during the festive season and thinner trading volumes that could amplify price moves, yet the author acknowledges that market mechanisms are opaque and that the effect could be a statistical artifact rather than a repeatable strategy.