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Type 1 diabetes results from the destruction of the cells in the pancreas that produce insulin, while type 2 diabetes is characterized by so-called "insulin resistance", presumably a reduced responsiveness of the body's tissues to the effect of insulin. More succinctly, in type 1 diabetes, insulin is not produced at all, while in type 2 diabetes, insulin is produced, but it is ineffective.

Based on this description, one would expect that type 1 and type 2 diabetes would look similar, with maybe type 2 diabetes being a milder form of the condition. This is not the case, however. The diseases are markedly different, at least when it comes to their effect on body weight.

Type 1 diabetes results in wasting:

a type 1 diabetes patient before and after insulin treatment - before, the individual is much thinner; afterwards, the individual is shown to be much less skinny

The images show a type 1 diabetes patient before and after insulin treatment.

In contrast, type 2 diabetes is associated with obesity, exactly the opposite scenario.

If the body does not respond to insulin in type 2 diabetes, why don't those afflicted waste away, in the way that (untreated) type 1 diabetes patients do?

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. $\endgroup$
    – Bryan Krause ♦
    Feb 17, 2020 at 16:49
  • $\begingroup$ I have changed your title to reflect the content of your question. How obesity produces type 2 diabetes is a valid question — it could well be asked separately — but is not what you are asking. $\endgroup$
    – David
    Mar 7, 2020 at 12:15

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The following is based on a conversation I had with a senior biochemist in my university who conducts grant-funded research on the relationship between diabetes and heart disease. It can be criticized for the paucity of external sources from which its veracity can be checked. However, although the question is based on a misconception I thought it should be addressed. Perhaps others could help improve the answer by supplying references etc.

The following points about Type 2 diabetes mellitus are relevant.

  • ‘Type 2 diabetes’ refers to a disease which encompasses conditions with a spectrum of severities.

  • This means that the description of it being “characterized by so-called ‘insulin resistance’” — alternatively expressed as cells being refractory to insulin — in fact means that there is a variation in the degree to which the cells are refractory. In many cases, although this leads to a higher blood sugar, it does not result in the complete breakdown of fat and muscle protein found in type 1 diabetes, where insulin is completely lacking.

  • Type 2 diabetes does not result in an increase in fat deposition and body weight. In many — but not all — cases it is caused by overweight.

  • In type 2 diabetes caused by overweight there is a gradual loss of fat. It is not apparent in a ‘snapshot’ of type 2 diabetics, many of whom have such large fat reserves that it will take a long time before these are broken down.

  • In severe type 2 diabetes the situation eventually becomes similar to type 1 diabetes as the beta cells of the pancreas can be destroyed. In these cases insulin injection is required.

  • Normally type 2 diabetes is controlled with drugs that reduce the glycemia — metaformin is currently the agent for the first line of treatment — and by lifestyle changes, especially in diet. (The treatment of type 2 diabetes was reviewed by Juan José Marín-Peñalver et al. in 2016 and considers their mechanisms of action etc..)

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  • $\begingroup$ In starvation, the breakdown of both fat and protein starts at the same time as soon as glycogen stores are depleted (source - p.385). Why would an untreated person with diabetes 2 on isocaloric diet lose weight (fat or muscles)? Two important reasons for wasted appearance in diabetes 1 are 1) loss of glucose due to glycosuria and 2) dehydration due to polyuria triggered by glycosuria. $\endgroup$
    – Jan
    Mar 12, 2020 at 10:39
  • $\begingroup$ @Jan — OK. The fat reserves are usually completely depleted before the protein, but I will take the phrase (mine not my source's) out. $\endgroup$
    – David
    Mar 12, 2020 at 11:44
  • $\begingroup$ It is still a parallel process. Initially, more fat than muscle will be lost, but at the time when fat stores are depleted, there will be already some loss of muscle. But the question is why would a person with diabetes type 2 lose weight at all when on isocaloric diet? $\endgroup$
    – Jan
    Mar 12, 2020 at 12:05
  • $\begingroup$ @Jan — You will notice that I waited three weeks before answering this question because of extreme pressure of a project I am working on. I felt I should try to answer as I had said I would in a comment apparently transferred to chat. I am still interested in improving my answer and finding appropriate biochemical sources, but it will be a week or two before I have time to do more than add comments. (The answer to your point would seem to lie in the hormonal control of fat turnover. I had thought that this would be through glucagon, but my colleague thinks not.) $\endgroup$
    – David
    Mar 12, 2020 at 13:41
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Type1 diabetes is an autoimmune disease where insulin producing cells are killed by the immune system. Many cells need insulin to be able to transport sugar from the blood. Without insulin they won't be able to use the blood sugar and people start to urinate sugar because of the high blood sugar levels. So the insulin levels will be low and the blood sugar levels will be high in type1 diabetes.

In the case of type2 diabetes the insulin production is not affected and cells cannot transport sugar fast enough, because they don't sense insulin properly. This results high insulin and high blood sugar levels. As the disease progresses, the insulin producing cells can die off and we can end up with a similar condition as we have in type1 diabetes.

Both have connections to weight. Insulin is a hormon that facilitates fat storage and fat conversion from sugar and it inhibits fat breakdown. So when insulin is low in type1 diabetes, then people have a hard time to gain weight. On the other hand insulin resistance is associated with obesity. So typically obese people suffer from type2 diabetes and they can lose weight as the disease progresses.

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  • $\begingroup$ If the tissues are refractory to insulin, that includes the adipose tissue, so your statement that the increased concentration of insulin prevents them losing weight doesn’t make sense, and according to my source is untrue. $\endgroup$
    – David
    Mar 12, 2020 at 8:14
  • $\begingroup$ @David You are right, I tried to find a reference for it, but failed. Probably it is just an urban myth. I edited my answer. $\endgroup$
    – inf3rno
    Mar 12, 2020 at 8:22
  • $\begingroup$ @David If it is any truth in that high insulin + IR causes weight gain, then probably it has something to do with leptin. I don't have time to investigate this. $\endgroup$
    – inf3rno
    Mar 12, 2020 at 8:42

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