Monday, April 21, 2014

High This, Low That

“The beginning of wisdom is the definition of terms”
- Socrates
High carb, low fat, moderate protein.  These are words to describe diets, but what do they mean?  The problem is that it really depends on how ‘high’, ‘low’ and ‘moderate’ are defined*.  For example: the Zone (30P:30F:40C) has been called a low carb diet, but is 40% carbohydrate really low?  Or is it simply ‘lower’ than the conventional guidelines and so should be described as a 'lower carb' diet. 

I’m going to propose some definitions for ‘high’, ‘moderate’ and ‘low’ to clear this up and base it on simplicity and some observations 

  • ~10% protein is essentially the RDI for the average person, which is the sufficient intake to meet nutrient requirements of 97-98% of the population [1]
  • Modeling has suggested that at least 15% protein is required to obtain sufficient micronutrients [2]
  • The recommended protein intake for chronic disease is 15-25% [1]
  • Protein intakes of 30-40% (depending who you speak to) and greater are thought to exceed the body’s ability to metabolise protein and/or get rid of urea
  • The average protein intake in Australia in about 16.5% [3].  You could argue that protein intake would be slightly higher if 35% [4] of calories didn’t come from junk food (high in refined grains (~10%), added fats and added sugar) 

Very Low
Very High

  • If moderate protein is 20% then it would be nice if moderate carbs + fat = 80%
  • There is an ongoing debate as to whether fat or carbohydrate is generally healthier.  At this point I don’t know, and probably no one does
  • Eating ~0% fat or carbs is doable (no need for dietary carbs, PUFA requirement is extremely low), although very restrictive and probably not too healthy.  Anyway, it would be more accurate to refer to such a diet as zero fat/carb
  • In PHD, the Jaminets calculated carbohydrate requirements (dietary or not, in the absence of ketosis) to be approximately 30% [5] 

Very Low
Very High

There are two main issues with this kind of classification: 

1.     A 1% increase in carbs from 47% to 48% magically results in the diet changing from a moderate carb diet to a high carb diet.  This is silly.  Think of the cut-off points not as thresholds, but as gradients
2.     These numbers are proportions, not absolute amounts.  The absolute amounts are more important to determine whether you’re getting enough of something.  In some circumstances the % can be misleading.  For example: an athlete on a low carb diet may eat more carbs than an inactive elderly person on a high carb diet like the dietary guidelines (45-65%) 

Finally ‘high’, ‘low’ and ‘moderate’ aren’t some judgment of whether a diet is ‘good’ or ‘bad’ 

* The field of diet is full of people using ambiguous labels to promote an agenda, for example: veg*ns say the SAD is high in animal protein and fat; mainstream dieticians say the SAD is high in red meat, SFA and salt; low carbers say the SAD is low fat and high carb; and everyone says the cliché of the SAD being high in sugar, fat and salt (if they choose their words poorly they might imply salt contains calories).  I heard a dietician say Australians eat a high meat diet and handed out some information suggesting we should eat 1 serve of meat per day.  You shouldn’t be surprised when you conclude that Australians eat a ‘high meat diet’ if you define ‘high meat’ as > 1 serve/day


  1. Four comments:

    * You're quite right that terms are ill-defined, different researchers use different and sometimes incompatible definitions, and that this is a stumbling block impeding scientific progress here. Thanks for writing about this.

    * Percentage-of-energy-intake is probably the wrong measure for macronutrients, for various reasons. One is that your body can, to some degree, mobilize stored fat as a substitute for dietary fat. Another is that protein requirements are dependent on lean body mass, growth, disease, pregnancy, exercise, but not dependent on fat mass nor on energy intake. Another is that the effects of keto seem to be triggered by a threshold which varies among different people but, as far as I can tell, isn't dependent on total energy intake.

    So, please write a new blog post which updates this to use absolute values instead and see if that changes your conclusions. ☺

    * Also, please see where we argue that recommendations such as the one you link to ([1]: are dangerously low on protein requirements. It suggests 0.84 g/kg for an adult man. That's probably so low that it would impair such a person's health.

    * "very restrictive and probably not too healthy. Anyway, it would be more accurate to refer to such a diet as zero fat/carb"; Disagree—I think zero carb is very healthy. I agree that it should be labeled "zero carb". As far as ketosis goes, it probably has the same effect as your "very low carb" category, but ketosis is probably not the only important effect of it.

    1. P.S. By "absolute values" I mean g/d/kg-body-mass or g/d/kg-ideal-body-mass, as we suggest on

    2. I chose percentages/proportions/ratios rather than absolute amounts because diets are mostly compared by the proportion of P:F:C calories. I agree with the protein requirements and the stored fat. Although stored fat independent of dietary fat would only be noteworthy during weight loss or on a very high carb diet (DNL).

      I agree and great blog post. The RDI is to avoid deficiency. With protein, from memory I think it's merely the level at which negative nitrogen balance doesn't occur. Many nutrients continue to improve health at levels above the RDI. Vitamin D is one of the better examples of this. Besides the RDI of protein is so low that it would take a raw vegan diet or a diet full of junk food to have an intake that low

      The 'probably not too healthy' is more about a lack of micronutrients, fibre and phytonutrients from a low intake of vegetables to have a carbohydrate intake that low, unless the diet is well planed

    3. You're right that the RDI is based merely on nitrogen balance, but it wrong even for that! See our comments about citations "[7]" and "[8]" on .

      > The 'probably not too healthy' is more about a lack of micronutrients, fibre and phytonutrients from a low intake of vegetables to have a carbohydrate intake that low, unless the diet is well planed

      I have long enjoyed your evidence-oriented posts on this blog, in which you investigate the evidentiary basis of claims instead of accepting them at face value. I would be interested to learn what evidence leads you to think that micronutrients, fibre, and phytonutrients (e.g. from eating vegetables) are important for health.

    4. If you're looking for well controlled RCTs with hard end-points I'm not aware of any. My thinking comes from fibre, phytonutrients and certain micronutrients seeming beneficial and difficult to get without plants. If I were to eat zero carb I wouldn't know, but I would be concerned about getting enough of certain micronutrients and not starving gut bacteria unless I planned it well.

  2. Whether higher carb or higher fat is more conducive to health depends on insulin resistance/sensitivity more than anything.
    As most people with health problems (rather than a bit more fat than they like to be seen with) are insulin resistant, that makes higher fat the healthier diet in a medical setting, but implies nothing about how the healthy should eat.

    1. True, it seems several medical conditions (like IR/T2D, NAFLD, cancer, neurodegenerative diseases) would likely get better with higher fat and lower carb

      This paper (cited by the Australian Dietary Guidelines) mentions that IR people lose more weight on low carb diets