The Science of Yo-Yo Dieting

Why Calorie Restriction isn’t everything when trying to get lean…

by James Honey, Pinnacle EAT Nutritionist


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The majority of people who ‘diet’ will fail to realise their goals and experience some form of ‘Yo-Yo effect’. This is due various prominent factors, a few of which are outlined below:

  • A major factor is that popular/trending/fad ‘diets’ will largely involve the complete exclusion of certain food groups or macronutrients. Firstly the psychology behind this is flawed and deserves a whole blog post on its own- tell a person to stop eating/doing something, without any specific strategy purpose or goal, and they will inevitably think about it more or just do it. Secondly, the body requires all macronutrients for optimal functioning. Whilst it may be able to survive without such, what would be the purpose of moving away from optimal function? And why would the removal of one food source (e.g sugar, fat, all carbohydrates!) without taking into account basic science (calories, metabolism, energy expenditure) have any measurable effect.
  • Dietary protocols (even those prescribed from industry professionals) can place too much focus on caloric deficit, and completely ignore the affect of the metabolism of the individual. As the human body is completely adaptive and never metabolically static, it is entirely at effect of an immeasurable amount of biological mechanisms and inputs (e.g training protocols, sleep, nutrient intake, nutrient timing and more). Of these we must control what we can, use evidence-based practice, and make modifications based on objective measurable data (bodyweight, body fat percentage, strength testing etc.).
  • People are not consistent. A person who is willing to take up the latest dietary fad or craze on a whim, and completely ignore decades of science, real life results and basic logic, is both unlikely to have good adherence to said ‘diet’ (poor emotional buy-in) and is likely to change on another equally flimsy whim. As with most things in life, consistency is key.

The Science – logical proof of metabolism:

The human body cannot infinitely shrink or grow due to food intake (although extremes can certainly be met). If this was the case, it would be possible for a man to grow to the size of a whale, or shrink to the size of a hamster. There is a stopping point, for the sake of survival and due to genetics.

Taking the above statement into account, it is logical to assess that the human body is adaptive, and will attempt to maintain homeostasis despite circumstances presented to it. The body wants to live, and will find a way to maintain life under extreme circumstances, such as very low calorie intake (at sacrifice to other areas of function). To an extent, this is exactly the concept of a ‘slow metabolism’ – put in simple terms, it slows down energy expenditure to slow down the inevitability of death (think of a pre-historic Homo-Sapien who hasn’t eaten for days, and needs to still hunt). It also slows down other areas, namely fat-loss (for energy storage), muscle gain (not a priority over living), general perceived energy levels, hormonal regulation and more.

It is then very easy to see why a Yo-Yo dieter is created in our modern society where food is readily available. As a case study, picture a person who wants to lose some fat. They choose their ‘diet’ and stick to protocol for a few weeks. After being in an extreme calorie deficit, the person may have lost a few kilograms. They then return to their previous eating habits. The increase in calories is too much for the now-slower metabolic rate, and more weight is put on that was previously held before the diet! What is worse, the person lost both muscle and fat mass, and only regained fat mass due to lack of stimulus for muscle growth.


Case Study:

  • Day 1 – 70kgs, 20% BF. Current diet at around 2400 calories/day, poor or random food choices.
  • Days 2 to 30 – Chooses diet at 1400 calories/day and adherence is 100% (e.g juice detox, only green foods or something equally as illogical)
  • Day 31 – 67kgs, 19% BF. Diet ends**. Body has metabolically adapted to maintain weight and function on 1400 calories/day. Likely in a nutrient deficit if specific macronutrients or necessary foods were excluded (think scurvy). Body has lost 3kgs, but only 1% BF (the rest is muscle mass as it does not store energy for survival like fat does).

**(please bear in mind your diet never ends until you die – you still need food!!)

  • Day 60 – 74kgs, 25% BF. After returning to 2400 calories/day, again with poor food choices, the body was in a 1000 CALORIE SURPLUS everyday! As a logical organism, the body stored the excess energy for later (as fat), and slowly worked to adapt to its new environment. Very little new muscle mass was laid down unless the correct training stimulus was provided.
  • OUTCOME – 60 days after beginning a fad diet (with good intentions), our person has starved miserably for 30 days, then gained 4kgs from starting weight, with less muscle mass and 5% more body fat than when starting! Process likely repeats for many years unless a true intervention occurs.

(Note. the calculations in the case study are only estimates and probably not mathematically accurate.)


How to do it properly

Nutrition must be approached with the adaptive nature of the human organism in mind. Firstly, a current baseline caloric level must be established. This will be a combination of a persons BMR (what they actually need), their current average daily caloric intake/energy expenditure (where they currently sit), and their adequacy of nutrient intake. From here, the desired purpose and goal will be established (e.g sports performance/body composition/more energy at work/general health and happiness with food). This will dictate the influence we must have over the measurable factors outlined in the introduction (training protocols, sleep, nutrient intake, nutrient timing and more).

A protocol may involve a small and carefully measured reduction in calories over an consistent timeframe, to elicit a small caloric deficit and influence the usage of stored fat, without losing muscle mass. Included will be a strength training program aimed at increasing muscle mass and achievement of any athletic goals, and all foods will be of a high quality and cover all nutritional requirements. Any larger reduction in calories over a shorter timeframe actually has a faster stop in body fat reduction, as the body and metabolism go into survival mode as outlined earlier!

A protocol may also involve slowly increasing caloric intake without changing body fat percentage, which is very possible with a carefully measured and applied approach over time. As the body is adaptive, we can train it to function on a large caloric intake which is optimal for body composition as there are more calories to reduce when weightloss/fatloss is desired (the person will not have to be malnourished and will actually achieve their goals!).

No matter their driving purpose and goals, every person will benefit from increased muscle mass/strength and a healthy range/lower body fat percentage. Malnourishment isn’t the answer. Specific, measurable and maintainable nutritional and training strategies that work with the body’s adaptive nature are. Above all, happiness and consistency are key!


“Eating ever less calories and doing gradually more exercise is a self imposed sentence to a lifetime of starvation, hateful exercise and bodyweight troubles” – Damon Hayhow, Recomp

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