Does Exercise Really Help You Lose Fat in a Healthy Way?

Introduction

Some people claim that reducing calories alone(basically “eating less”)is all you need to lose weight.
They says: “Isn’t exercise overrated for dieting? If I simply cut my daily calories, won’t I lose the same amount of weight?”

The study introduced below puts this question to the test, focusing not just on body weight, but also on body composition.
In other words, whether you lose mainly fat or also sacrifice muscle mass.
Because from a long-term health perspective, preserving muscle mass is crucial (it boosts metabolism, strength, and overall functionality) while losing weight.
Muscle mass helps maintain your metabolic rate. Losing too much muscle can weaken the body, slow metabolism, and lead to poorer health outcomes. Thus, “healthy” weight loss typically aims to maximize fat loss while minimizing muscle loss.

Below is a brief article-style summary of a randomized controlled trial by Hernández-Reyes et al. (2020), which looks at the role of different exercise intensities—on top of a hypocaloric (reduced-calorie) diet—among overweight or obese women.

About the Study

Participants

   - 117 adult women (average age ~43), all overweight (BMI ≥25) or obese (BMI ≥30).

   - Initially sedentary, not on any restrictive diet in the previous 6 months.

   - Key measure: not just weight, but specifically body fat percentage (%BF) and muscle mass (MM).

Overall Goal

   -  To see whether adding moderate or intense physical activity (PA) to a 6-month diet plan (-500 kcal/day) impacts fat loss and muscle retention, compared to simply dieting with minimal exercise.

Detailed Group Classification

All participants followed the same low-calorie diet, which was about 500 kcal/day less than their usual intake. They were then randomly split into three groups:

1. Sedentary, CON (Control, Minimal Exercise)

   -  Essentially no additional exercise prescribed.

   -  Low-level activity (1–4 METs), e.g., short walks (≤30 min). 

2. Moderate, MPA (Moderate Physical Activity)

   -  Target of 10,000 steps/day (~60 min of walking),

   -  Equivalent to moderate intensity (5–8 METs, about 60% VO2max).

3. Intensive, IPA (Intense Physical Activity)

   -  Three sessions/week of high-intensity training (>8 METs).

   -  Specifically, BodyPump-style workouts with resistance & aerobic components.

   -  On non–BodyPump days, participants also took ~1-hour walks at moderate pace, matching the weekly exercise volume.

Study Method Overview

Duration: 6 months (24 weeks).

Diet:

   -  Each woman’s daily calorie intake cut by ~500 kcal (hypocaloric).

   -  Approx. macronutrient ratios: ~25–30% protein (1.8 g/kg recommended), 40–45% carbs, 30–35% fat.

Measurements:

   -  Body weight, body fat (%BF), and muscle mass (MM) tracked at baseline (0 wk), 3 months, and 6 months.

   -  Bioelectrical Impedance Analysis (BIA) used to assess %BF and MM.

   -  Physical activity levels monitored via smartphone pedometer app (Accupedo).

Data Analysis:

   -  Compared final changes (particularly at 6 months) among the three groups.

Results

At the end of 6 months, all groups lost weight to some extent. However, major differences emerged when looking at body fat reduction and muscle mass:

(Fig. Modification of body composition at 24 weeks depending on the physical activity prescribed in combination with hypocaloric diet)

   -  Sedentary(CON), with no extra exercise, did lose weight (~6% of body weight) but also lost a significant amount of muscle mass (over 3 kg on average).

   -  Moderate(MPA) group lost more body fat (~10.57% drop in body fat percentage) and also lost slightly less muscle mass than the control—though muscle loss was still notable.

   -  Intense(IPA) group showed the greatest body fat reduction (over 16% drop!) and, amazingly, ended up gaining ~1 kg of muscle despite being in a calorie deficit.

Below is a summary table focusing on 6-month changes:

Conclusion

Based on these findings, just eating less will help shed pounds in the short term, but adding physical activity dramatically improves body composition.
If your aim is a healthy diet-driven weight loss that maximizes fat reduction while preserving (or even building) muscle, exercise is a must.
Intense routines (resistance + cardio) were the most effective in this study, but even moderate activity was better for burning fat than dieting alone.

So, is exercise really good for healthy fat loss?
Yes, if you want to lose fat and keep your muscle (and metabolism) strong, it absolutely is.