How a San Diego Sports Nutritionist Builds a Fat-Loss Plan: Macros, Protein, and the Science Behind Body Composition Change

Step 1: Calculate Your BMR + TDEE

Every effective fat-loss plan starts with knowing where your calorie ceiling actually sits. We use the Mifflin-St Jeor equation — the most accurate predictive equation for resting energy expenditure across the general population (Frankenfield et al., 2005).

Once we have your BMR, we multiply by an activity factor (1.2-1.9) based on your real weekly movement. The result — your TDEE — is the calorie intake that maintains your current weight. Fat loss happens below it. Muscle gain happens above it.

Our free BMR + macros calculator runs these numbers in 60 seconds and gives you a personalized starting point.

Step 2: Set Your Calorie Deficit

The biggest mistake in fat loss is going too aggressive too fast. Severe deficits (40%+ below TDEE) drive short-term scale movement but at the cost of muscle loss, metabolic adaptation, and adherence collapse.

For sustainable fat loss with muscle preservation, the research supports a 15-25% deficit. Combined with structured training and adequate protein, this range allows for fat loss of roughly 0.5-1% of body weight per week — slow enough that the body doesn’t fight back, fast enough to feel like progress.

Step 3: Set Protein First, Then Build the Rest

Protein is the single most important macro for fat loss. It preserves lean mass in a calorie deficit, drives the highest thermic effect of food (TEF), and produces the strongest satiety response per calorie.

The evidence base for protein intake during fat loss is unusually strong. Morton et al.’s 2018 meta-analysis of 49 studies established a plateau at 1.62 g/kg of body weight per day for muscle protein synthesis benefits — with the confidence interval extending up to 2.2 g/kg for individuals with high training stimulus or aggressive deficits.

Practical Protein Targets

• 180 lb client wanting fat loss with muscle preservation: 135-160 g protein per day
• 150 lb client wanting fat loss: 110-130 g protein per day
• Distribute across 3-5 meals for optimal muscle protein synthesis (Schoenfeld & Aragon 2018)
• Higher protein during aggressive deficits — up to 2.4 g/kg for short-duration cuts in lean clients

Step 4: Set Carbs and Fats Around Training

Once protein is set, the remaining calories are split between carbohydrates and fats. The split depends on training intensity, sleep quality, and individual preference — there’s no universal “best” ratio.

Training-Day Carbohydrate

For clients training 2-3x per week, we typically target 2-4 g of carbohydrate per kg of body weight on training days, weighted toward the meals before and after sessions. Carbohydrate availability around training preserves performance, supports glycogen replenishment, and protects training quality during fat loss.

Fat Floor

Fat shouldn’t drop below 0.5-0.8 g/kg/day — needed for hormonal health, fat-soluble vitamin absorption, and satiety. For most clients, fat ends up at 25-35% of total calories.

Step 5: Sleep, Stress, and Adherence

The macros are the math. Adherence is everything else. The clients who get the most out of their fat-loss plan are the ones who treat sleep and life stress as programmable variables — not as afterthoughts.

Sleep restriction below 7 hours per night has been shown to blunt muscle protein synthesis, reduce testosterone, impair glucose tolerance, and shift food intake toward energy-dense, low-protein foods — even when training and nutrition are perfectly calibrated. Sleep is part of the plan, not a separate problem.

Step 6: When to Add Functional Lab Testing

For some clients, the macros are right but the results stall. When that happens, we look deeper. Functional lab testing can identify the metabolic or gut-health factors that are limiting your response to a clean nutrition plan:

• Microbiome panels — dysbiosis, low diversity, or specific pathogens that affect nutrient absorption and inflammation
• Hormone testing — thyroid, cortisol, sex hormones that influence body composition
• GI inflammation markers — calprotectin, secretory IgA, gut barrier integrity
• Food sensitivity panels — IgG-mediated reactions that drive inflammation and water retention

This isn’t necessary for most clients — but for the 20-30% whose results stall on a clean plan, it’s often the difference between continued effort and meaningful change.

How We Translate the Science Into Your Plan at PTC

Every client at Performance Training Center gets a fat-loss plan built on this foundation:

• Mifflin-St Jeor BMR + TDEE calculated from your weight, height, age, sex, and activity
• 15-25% moderate deficit calibrated to your training, life stress, and adherence capacity
• Protein at 1.6-2.2 g/kg of body weight distributed across 3-5 meals
• Carbohydrate periodized around training days for performance preservation
• Fat at 25-35% of total calories with a floor of 0.5-0.8 g/kg for hormone health
• Sleep and stress treated as nutrition variables alongside the macros
• Functional lab testing on demand when standard macros aren’t producing change
• Designs for Health practitioner-grade supplementation at our dispensary with client pricing

About Performance Training Center

Performance Training Center is a private one-on-one training studio in San Diego’s Bankers Hill, founded by Martin Alonzo — Certified Personal Trainer, Strength & Conditioning Coach, Certified Nutritionist, CHEK Practitioner, Golf-Specific Strengthening Coach, Destination Wellbeing Practitioner, and Somatic Therapist with over 22 years of experience.

Nutrition coaching is integrated into every training program — for clients across La Jolla, Downtown San Diego, Coronado, Encinitas, Carlsbad, Del Mar, Rancho Santa Fe, and beyond.

Individual results vary based on ability, program intensity, recovery, and individual adherence. No specific outcome, timeline, or transformation is guaranteed. This article is educational and is not medical or nutritional advice for an individual. Consult a licensed healthcare professional before making changes to your nutrition or training program.