What does protein do?
Protein is an essential macronutrient that plays many important roles in the body. Here are some of the key functions of protein:
- Builds and repairs tissues and cells – Protein is the building block of muscles, bones, skin, hair, and nearly every other part of the body. Getting adequate protein is crucial for rebuilding and repairing tissues, especially after exercise.
- Makes enzymes, hormones and antibodies – These protein-based substances control almost all bodily processes including metabolism, DNA replication, and oxygen transport. Protein is vital for making these crucial components.
- Transports nutrients and maintains fluid balance – Proteins act as transporters in the blood and carry important nutrients like iron to cells. Proteins also maintain fluid balance between the blood and tissues.
- Provides energy – When carbohydrate intake is low, protein can be used for fuel. But it’s not the preferred energy source as protein is primarily needed for its other roles.
In summary, protein is involved in just about every bodily function. It plays a structural role and makes regulatory substances. Protein is so fundamentally important that a deficiency can impair immunity, metabolism, organ function, and many other systems.
How much protein do we need daily?
The recommended daily intake (RDI) for protein is 0.8 grams per kilogram of body weight or 0.36 grams per pound. This equates to:
- 56 grams per day for the average sedentary man
- 46 grams per day for the average sedentary woman
However, research shows that higher intakes may be beneficial, especially for active individuals. Here are suggested protein targets based on activity level:
| Group | Protein Intake |
|---|---|
| Sedentary | 0.8 g/kg or RDI |
| Moderately Active | 1.0-1.2 g/kg |
| Very Active or Athletes | 1.4-2.0 g/kg |
As an example, a 150 pound moderately active person would need 68-82 grams of protein daily (1.0-1.2 g/kg x 150 lb converted to kg).
Higher protein intakes have been shown to help build and maintain muscle mass, aid post-workout recovery, optimize body composition by reducing fat mass, and support fat loss during calorie restriction.
Do protein needs change on rest days?
Protein needs do not dramatically change on rest days versus training days. Here are two reasons why protein intake should remain high even on rest days:
Muscle repair and growth still occurs
Exercise, especially strength training, causes small tears and damage to muscle fibers. The body then repairs and reinforces the muscles during rest days, leading to growth and increased strength over time. This muscle protein synthesis is stimulated by protein consumption. Consuming adequate protein on rest days provides the amino acids to facilitate muscle repair and growth.
Prevents muscle breakdown
On rest days, the body is no longer in a muscle building state like on workout days. Lack of protein intake on rest days can lead to a net breakdown of muscle proteins. Getting sufficient protein even at rest prevents catabolism and maintains lean muscle mass.
For these reasons, protein intake does not need to be drastically reduced on rest days for those who are actively strength training. The anabolic, anti-catabolic effects of protein are still needed, albeit to a slightly lesser degree than on heavy training days.
Should protein intake be slightly reduced on some rest days?
While protein needs do not change hugely between training and rest days, there are some cases where a slight reduction in protein intake on some rest days would be appropriate:
- Very high protein takers – Those who normally consume more than 1.6 g/kg daily may benefit from a 10-20% reduction on some rest days for cost savings or reduced strain on the kidneys.
- Intermittent fasting – When using fasting protocols like alternate day fasting, protein can be reduced on fast days to accommodate lower calorie intake.
- During fat loss diets – Lowering protein and overall calories periodically can give metabolism a break and allow leptin to rebound during aggressive cuts.
Here is an example protein intake schedule with slightly reduced protein on some rest days:
| Day 1 | Day 2 | Day 3 | Day 4 | Day 5 | Day 6 | Day 7 |
|---|---|---|---|---|---|---|
| Training | Rest | Training | Rest | Training | Rest | Rest |
| 1.6 g/kg | 1.2 g/kg | 1.6 g/kg | 1.2 g/kg | 1.6 g/kg | 0.8-1.0 g/kg | 0.8-1.0 g/kg |
This allows for adequate protein on training and standard rest days but has a moderate reduction on some rest days.
Summary
Here are the key takeaways on protein intake needs on training versus rest days:
- Protein supports muscle growth and repair and should not be drastically cut on rest days.
- Aim to consume close to your standard protein intake even on rest days.
- There is some flexibility to reduce protein moderately on some rest days to allow metabolic rest.
- Use training days to reach the higher end of your protein intake goals.
- Adjust protein intake based on your specific goals and response.
Getting sufficient protein every day is key, but intake can be optimized by strategically consuming a little more protein on heavy training days versus lighter rest days. This helps facilitate muscle repair and growth while allowing for metabolic breaks.