Intermittent Energy Restriction - What is it and Does it Work?

When it comes to dieting, there are many approaches that you can take. Intermittent energy restriction (ER) is one of them!

What is it?

Intermittent ER involves short periods of energy restriction, or eating in a calorie deficit, interspersed with periods of energy balance, ie. Eating at your maintenance calories.

Is it the same as intermittent fasting?

Intermittent ER is somewhat similar to alternate day fasting or intermittent fasting, with the main difference being that intermittent ER usually takes place over blocks of time, such as a number of days or weeks.

What are the proposed benefits of intermittent ER?

There are a number of proposed benefits to taking this dietary approach.

1. Reductions in metabolic adaptation to dieting

A key benefit is that it is proposed to attenuate the negative effects of dieting on our metabolism and body. When in a calorie deficit, a number of mechanisms kick in which act as our body’s defence against fat loss. This is known as “adaptive thermogenesis” or metabolic adaption to dieting. These mechanisms are both biological and behavioural in nature and include:

- A reduced resting energy expenditure (REE), which means our energy output and the overall calories we burn are lower

- Increases in appetite due to increased ghrelin levels (our hunger hormone)

- reduced levels of satiety or fullness due to reduced levels of circulating leptin (our fullness hormone)

- Reductions in non-activity exercise thermogenesis or NEAT levels due to decreases in energy

Intermittent ER is thought to reduce these negative side effects from your body’s metabolic adaption to dieting as you are not eating in continuous calorie deficit, and instead have periods of higher maintenance calories. It is thought to have a particularly protective effect on preventing major reductions in our body’s REE.

Another benefit of intermittent ER is that it may result in increased dietary adherence. Dieting can be hard, and there are times when hunger levels may be higher, and overall adherence is lower. Intermittent ER has the dual benefit of helping to manage appetite, and manage adherence due to the periods of energy restriction being shorter and interspersed with periods of eating at maintenance calories.

What does the science say?

A key study focusing on intermittent ER is the MATADOR study. This study involved 51 men with obesity who were randomised to 16 weeks of either: (1) continuous (CON), or (2) intermittent (INT) energy restriction (ER). The intermittent ER was completed as eight 2- week blocks of ER alternating with seven 2-week blocks of energy balance (30 weeks total). Both groups had a 33% reduction in their total daily energy intake meaning the percentage calorie deficit was the same in both groups. The intermittent ER group received their maintenance calories during the with seven 2-week blocks of energy balance, or ‘rest periods.’

The results found that greater weight and fat loss was achieved with intermittent ER. The authors concluded that interrupting dieting with energy balance ‘rest periods’ may reduce compensatory metabolic responses and, in turn, improve weight loss efficiency.

What can we conclude about intermittent ER?

Intermittent ER may be a useful approach when looking at a long and slow fat-loss phase. However, it is a new concept and it has not been completely studied yet. There are gaps in the literature, such as studies looking at intermittent ER in athletes. There are also differences in the protocols used in studies, such as the length of ‘rest periods’ or eating at maintenance - some studies use a period of 2-weeks, whereas others only use a few days. More research is needed but we think it’s a pretty interesting approach to consider!

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